Steve Castle Torry Hill Farm Park View Manor Road Milstead Kent ME9 0SF

Transcription

1 Project Number: TF 17 Project Title: Plums: To determine the performance of 6 new plum varieties Project Leader: Tim Biddlecombe Farm Advisory Services Team Ltd. Brogdale Farm Brogdale Road Faversham Kent ME13 8XZ Contractor: Industry Representative: Steve Castle Torry Hill Farm Park View Manor Road Milstead Kent ME9 SF Report: Final report, January 213 Start Date: 1 st October 27 End Date: 31 st March 213

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3 CONTENTS GROWER SUMMARY... 1 Headline... 1 Background and expected deliverables... 1 Summary of the project and main conclusions... 1 Financial benefits... 7 Action points for growers... 8 SCIENCE SECTION... 9 Introduction... 3 Materials and methods... 1 Results Cultivar summaries Conclusions Technology Transfer References... 35

4 GROWER SUMMARY Headline Six plum varieties have been tested for their suitability for production in the U.K. The project spanned across four fruiting years, from 29 through to 212 and during this period three varieties have been identified which show commercial potential. Background and expected deliverables A number of new plum varieties (Prunus domestica) from mainland Europe have potential for UK production. The purpose of this project was to assess the commercial potential of these new varieties in respect of yield and fruit quality. In addition, their seasonality was determined. The trial was assessed and recorded between 29 and 212. The varieties included,,, Anita, and and were compared to and as standards. Each variety, with the exception of, was grown on two rootstocks St. Julian A and (Ferlenain). The project aimed to identify which, if any of these varieties, show potential for commercial production in the U.K. Summary of the project and main conclusions The trial was conducted at Brogdale Farm, Faversham, Kent and was planted during winter 28. Six new varieties were planted with two standard varieties ( and ) included as control varieties to which the new varieties were compared. Certain varieties started fruiting in 29, but all fruited from 21 until 212. The total yields, fruit number per tree and percentage marketable fruit for 21, 211 and 212 are presented in Figures 1-3 below. The dates of first pick and cropping sequence of the varieties for 21, 211 and 212 are presented in Table 1 below. Other records collected included date of bud break, flowering, start of fruit development, fruit number, fruit size and total soluble sugars. This information is all set out in the science section of this report. 1

5 Anita Total yield (kg) Anita Total yield (kg) Total yield per tree

6 Anita Number of fruit Anita Total yield (kg) Figure 1. The total yield produced per tree by each variety/rootstock combination in 21, 211 and 212. Standard error bars are shown. Number of fruit per tree

7 Anita Number of fruit Anita Number of fruit Figure 2. The total number of fruit produced per tree by each variety/rootstock combination in 21, 211 and 212. Standard error bars are shown. 4

8 Anita Percentage marketable fruit (%) Anita Percentage marketable fruit (%) Percentage marketable fruit

9 Anita Percentage marketable fruit (%) Figure 3. The percentage marketable fruit produced per tree by each variety/rootstock combination in 21, 211 and 212. Standard error bars are shown. Harvest season Table 1. The date of first pick for each variety from 21 to 212. Picking sequence is also given with the earliest variety assigned order 1 and the latest variety order 7. Cropping Cropping Cropping 21 Sequence 211 Sequence 212 Sequence 5-Aug 1 13-Jul 1-5-Aug 1 2-Jul 2 1-Aug 1 Anita 9-Aug 2 25-Jul 3 9-Aug 2 17-Aug 3 25-Jul 3 2-Aug 3 25-Aug 4 15-Aug 4 3-Aug 4 7-Sep 5 17-Aug 5 8-Sep 5 6

10 Cropping Cropping Cropping 21 Sequence 211 Sequence 212 Sequence 1-Sep 6 29-Aug 6 16-Sep 6 15-Sep 7 6-Sep 7 19-sep 7 Main conclusions The trial has identified, and as having potential for U.K. production. For, its main positive attribute was the fact that it was the earliest new variety in the trial, with harvest starting at the same time or just before. was the latest variety, and started fruiting around the same time as Marjorie s Seedling grown in the Faversham area. Its yield was generally consistent and fruit size was good. stood out due to its exceptional flavour. This was partly due to it having the highest o Brix of any variety in the trial. However, its sometimes low and inconsistent yield across the four fruiting years would make commercial production difficult. For example, in 211 its yield was one of the highest of the new varieties, but in 21 and 212 it only produced 5 or less fruit per tree. Other varieties had specific traits which may make them sufficiently attractive to U.K. growers. For example, fruit size in Anita was larger than the other varieties and it has useful crop timing, falling between and. also had similar attributes to and cropped a few days earlier than, giving rise to the potential for an extended plum season. The fruit quality of was not acceptable. There is potential for supplementing the limited range of varieties currently grown in the UK with some of the varieties being tested here and potentially extending the season with the earlier and later varieties, such as and respectively. Financial benefits The availability of new varieties to spread the season and reduce the need for short term storage of plums could offer some potential savings in energy costs. 7

11 Action points for growers All of these varieties have shown promise for commercialisation but further trialling on a large scale in a number of different locations is needed due to annual variability. Growers might consider planting trial blocks on their own sites of the better performing varieties: is an early variety producing fruit at approximately the same time as and with fruit that is similar to the appearance and flavour of, although its yield was generally poor is harvested around the same time as Marjorie s Seedling and is the latest of the varieties tested in this trial. The fruit are large with good flavour and yields were among the highest of those being tested has an exceptional flavour but its yield differed considerably from year to year Anita may also be worth trialling in larger blocks simply because of its early timing and large fruit size 8

12 SCIENCE SECTION Introduction There has been recent development of new plum cultvars (Prunus domestica) in Europe that show potential for U.K. production. The purpose of this project was to assess the commercial potential of these new cultivars in respect of yield and fruit quality as well as season. In addition, seasonality of these cultivars was determined. Crossings between Stanley and Borssumer, which is known as Ortenauer in the southern regions of Germany, resulted in the selection of in This was the first genotype completely resistant to Sharka disease i.e. the plum pox virus (PPV) (Hartmann, 1999). It is primarily because of its PPV-resistance in outdoor tests that this cultivar was selected. However, it is also precocious, self-fertile and has high, regular yields. The ripening time of is identical with the cultivar Hauszwetsche, or sometimes slightly earlier. The fruits are of medium size, 4-5 g average fruit weight and have a sugar content of 16 to 18 %. This is a recent release from the Hohenheim programme in Germany. It was selected for this project primarily because it was one of the latest cultivars available. was originally selected as a large blue plum with good flavour and partial resistance to PPV. It is a lateseason plum. Sudar et al. (211) compared sugar content in a number of continental plum cultivars, including and. had higher sugar content than, particularly towards the end of cropping. This cultivar originated from a cross between Hall and Ruth Gerstetter and was selected in 1974 in Yugoslavia (as it was then) and released in was selected because it produced regular high yields of large fruit around 43mm in diameter. The skin is moderately thick and deep blue in colour. In the Balkans the fruit ripens in late July/early August (Ogasanovic, 1991). This cultivar originates from France. Unfortunately no data is available in the published literature on its characteristics. 9

13 This cultivar was bred at INRA in Bordeaux, France and originated from a cross of the greengage Reine Claude Verte pollinated with California Blue in It was selected primarily because of its flavour, although the fruit size was deemed large and in Bordeaux it was an early variety. In Bordeaux fruit is harvested between 1th and 15th August and note is made of its resistance to cracking (Renaud and Lafargue, 1998). Anita This cultivar was bred and developed in Sweden and is the result of a cross between Early Laxton and Ruth Gerstetter. This project aimed to assess these six new cultvars. They were grown on two rootstocks and comparisons over four years have been made. This assessment of the potential of these new cultivars in a commercial situation has resulted in recommendations on their suitability for commercial production in the UK. Data from 211 shows important differences to the previous years, which resulted in changed conclusions on one or two of the new cultivars. Materials and methods In 27 the scion cultivars were grafted to St. Julian A and (Ferlenain) rootstocks by Frank P. Matthews, Tenbury Wells, Worcestershire. Trees of six cultivars were delivered to FAST Ltd. at Brogdale to be planted in the trial site in winter 28. The trees were planted at a spacing of 1m within the row and 3m between rows. Table 2. The variety/rootstock combinations included in the project. St. Julian - Anita Anita - 1

14 The trial was conducted at Brogdale Farm, Faversham, Kent in an orchard specifically planted for this project. The soil is generally clay over flint and the farm does not have irrigation. A soil analysis was conducted prior to planting which showed magnesium and ph as optimum, phosphate as low and potassium as high. As a result, triple super phosphate was applied at the rate of 24kg/ha. Table 3.The soil characteristics for the trial plot Soil ph Sample depth Soil type Magnesium (ppm) Phosphate (ppm) Potassium (ppm) 6.9 to 15 cm Clay loam was the trees first fruiting year for certain cultivars, but only in 21 did all the cultivars start to produce fruit. Assessments of fruiting and growth were conducted to determine the characteristics of each cultivar and data are presented here from 21 through to 212. Yield per tree was recorded as marketable and non-marketable fruit. Marketability was determined by fruit appearance and not by fruit size. Fruit size was assessed in two ways, by recording both the average diameter of 5 fruit per cultivar and the average weight of fruit from each tree. At fruit ripening, total soluble solids level ( o Brix) was recorded by cutting the fruit in half vertically and squeezing the juice from one half onto a refractometer. The dates of bud break, flowering and first pick were also recorded for each cultivar. Trees were pruned and trained as normal commercial best practice. However, no fruit thinning was conducted as this would disguise any differences between cultivars in fruit number and in fruit size. Results Total yield per tree achieved high total yields in every year, significantly higher than all the other cultivars, and reached 16kg in 211 (Figure 4). This was primarily due to fruit number rather than fruit size. Normally would be thinned by growers but in this trial, none of the cultivars were 11

15 Anita Total yield (kg) Anita Total yield (kg) thinned so that the results would not be confused by the level of thinning and as a result fruit size suffered in each year for

16 Anita Total yield (kg) Figure 4. The total yield produced per tree by each variety/rootstock combination in 21, 211 and 212. Standard error bars are shown. had a fairly consistent and intermediate yield in each year and achieved yields which fluctuated between 3kg and 6 kg. As the trial progressed the difference in yield between the two rootstocks became more significant, with on St. Julian out-yielding on. Of the new cultivars, it was perhaps that performed best as far as yield was concerned. Over the course of the project it produced a relatively consistent yield and was one of the highest yielding of the new cultivars, and again, on St. Julian it produced higher yields than on. produced very variable yields with the highest yield seen in 211. In 21 and 212 yields were about 1% of the 211 yields. This variability suggests a tendency towards bienniality and work is needed to determine whether a sustainable annual yield could be achieved. This cultivar does have one of the best flavours of those trialled but could only be considered for commercial production on any scale if this variability in yield was addressed. The least successful cultivars in terms of overall yield were and, which produced less than 3kg every year. produced fruit of good quality at about the same 13

17 time as, and so despite its disappointing poor yield the cultivar did show some promise for commercial production. Similar yield differences between the two rootstocks were seen in a number of cultivars, with resulting in a lower yield than St. Julian. Number of fruit per tree, and did not produce any fruit in 29, and furthermore also did not fruit in 212. This is important because it crops early, at a useful time of year and fruit quality is generally good. The climate in 212 was poor for plums but seemed to be more sensitive than the other cultivars tested. Anita and produced the least number of fruit per tree with their fruit numbers across the years being generally less than 5 fruit per tree. This reduction may have contributed to the large fruit sizes of both cultivars. produced very variable numbers of fruit over the course of the project, with 211 being the only year where a sensible number of fruit was produced by the trees. In 21 and 212 very few fruit were produced, again suggesting that the cultivar has a tendency towards bienniality. The largest fruit number observed was for, which from 21 onwards achieved fruit numbers in excess of 2 fruit per tree per year. This would have been lessened by thinning commercially and the high fruit number did impact fruit size. It is an important point that the new cultivars tested did not need to be thinned, possibly with the exception of in 211. also produced relatively large numbers of fruit per tree, reaching numbers in excess of 2 in 211, again suggesting thinning would have been needed. Throughout the four years also produced relatively large numbers of fruit, particulalry in 29 and 21, although fruit size was smaller than the other cultivars. However the number of fruit decreased when the fruit size became larger from 211 onwards. Generally, fewer fruit were produced by the cultivars on than on St. Julian (Figure 5). 14

18 Anita Number of fruit Anita Number of fruit

19 Anita Number of fruit Figure 5. The total number of fruit produced per tree by each cultivar/rootstock combination in 21, 211 and 212. Standard error bars are shown. Percentage marketable fruit and showed the highest percentage of marketable fruit consistently across all years, with an average percentage of between 8% and 9%. s consistency in yield, as well as its high percentage of marketable fruit, suggests that it may be a suitable cultivar for commercial production. The most successful year for producing marketable fruit was 211, when all cultivars produced more than 75% marketable fruit, and this suggests that all of the new cultivars may be considerably influenced by the favourable environmental conditions which occurred during that year (Figure 6). Anita and in particular produced the lowest percentage marketable fruit in the remaining years, 21 and 212. For, this was mainly due to fruit russetting and particularly in 21 fruit cracking. In that year there was considerable rainfall just as harvest started, which caused cracking of the fruit at the calyx. This was worse on than on St. Julian. 16

20 Anita Percentage marketable fruit (%) Anita Percentage marketable fruit (%)

21 Anita Percentage marketable fruit (%) Figure 6. The percentage marketable fruit produced per tree by each cultivar/rootstock combination in 21, 211 and 212. Standard error bars are shown. Fruit diameter The fruit diameter of the new cultivars ranged between 4mm and 5mm across the years, with the exception of, which had an average diameter of approximately 3mm in 29 and 21 until considerable increases in fruit diameter up to 4-5mm from 211 onwards. Of the new cultivars Anita consistently achieved the largest fruit diameter of 5mm, closely followed by with a diameter of between 45 and 5mm. For both cultivars, this was perhaps their main positive attribute, and particularly for Anita this may make the cultivar worth planting. The new cultivars had an average fruit diameter which was greater than those of the established cultivars and, suggesting that thinning of these new cultivars may not be necessary. This would certainly be of benefit to plum growers. For example, reached an average fruit diameter of 3mm and this was consistent across the four years. Similarly, had an average diameter of 35mm to 4mm across the four year span. However, these would be too small for many retailer specifications and so and are thinned commercially every year to improve fruit size (Figure 7). 18

22 Anita Fruit diameter (mm) Anita Fruit diameter (mm)

23 Anita Fruit diameter (mm) Figure 7. The average fruit diameter of fruit produced per tree by each cultivar/rootstock combination in 21, 211 and 212. Standard error bars are shown. This may not be the case with the newer cultivars such as where fruit size is maintained without thinning, even when the fruit number increased, for example in 211. Obviously this will depend on the retailer specifications for these new cultivars if and when they are grown commercially. The fruit diameter of the cultivars did not tend to vary significantly and consistently between the different rootstocks. Fruit size The average fruit size for the new cultivars generally ranged between 4g and 6g. However and both produced some of the smallest fruit throughout the four years, with the average size of fruit at approximately 3g and from 3-4g. Again, this demonstrated the need for thinning of these cultivars (Figure 8). 2

24 Anita Fruit size (g) Anita Fruit size (g)

25 Anita Fruit size (g) Figure 8. The average fruit size of fruit produced per tree by each cultivar/rootstock combination in 21, 211 and 212. Standard error bars are shown. The large diameter of the fruit produced by Anita was reflected by its large size, which varied between 7g and 9g. also showed a relatively large fruit size, with the exception of 21 where the fruit size was considerably reduced from 6g to 4g, displaying variability in fruit size even though fruit number was not particularly high in this year. had the smallest fruit size of the new cultivars, averaging 4g. This, together with its variable yield, means that methods of improving the crop will need to be found before commercial plantings are made on any scale. s fruit size tended to be considerably different between the two rootstock types in 212, with St. Julian averaging a fruit size that was on average 2g more than that produced on. However the other cultivars did not generally have a substantial difference between rootstocks. Total soluble solids The average o Brix for the cultivars tended to range between 15 o and 25 o. Whilst Anita did produce a reasonably high marketable yield and large fruit, its fruit had the lowest o Brix, averaging 15 o. This was similar to the o Brix of and (Figure 9). 22

26 Anita TSS ( o Brix) Anita TSS ( o Brix)

27 Anita TSS ( o Brix) Figure 9. The average total soluble solids (TSS) of fruit produced by each cultivar/rootstock combination in 21, 211 and 212. Standard error bars are shown. and showed the highest o Brix levels, achieving a o Brix of between 2 o and 25 o, indicating a good fruit quality and taste. Certainly in the samples supplied to retailers as well as growers visiting the trial site, the flavour of and were both well regarded. Bud break and flower development The main reason for recording bud development stages was to determine whether crosspollination would be an issue with any cultivar due to differences in flowering dates. Whilst the dates of bud break, pink bud and full bloom did vary slightly between cultivars this was not consistent between years and it was really only in 21 that there were any sizeable differences between cultivars. There appeared to sufficient overlap in flowering period in each year to allow cross pollination between the cultivars (Tables 4-6). 24

28 Table 4. The date of bud break, pink bud, full bloom and fruitlet stage for each cultivar/rootstock combination for 21. Date of bud break Pink bud Full bloom Fruitlet 23-Mar 14-Apr 21-Apr 19-May Anita 17-Mar 14-Apr 21-Apr 19-May 23-Mar 21-Apr 21-Apr 19-May 17-Mar 14-Apr 21-Apr 12-May 1-Apr 14-Apr 21-Apr 12-May 23-Mar 14-Apr 21-Apr 19-May 23-Mar 14-Apr 21-Apr 19-May Table 5. The date of bud break, pink bud, full bloom and fruitlet stage for each cultivar/rootstock combination for 211. Date of bud break Pink bud Full bloom Fruitlet 7-Mar 21-Mar 4-Apr 2-May Anita 7-Mar 21-Mar 28-Mar 2-May 7-Mar 21-Mar 4-Apr 2-May 7-Mar 21-Mar 4-Apr 2-May 7-Mar 21-Mar 4-Apr 2-May 7-Mar 28-Mar 4-Apr 2-May 7-Mar 21-Mar 4-Apr 2-May 25

29 Table 6. The date of bud break, pink bud, full bloom and fruitlet stage for each cultivar/rootstock combination for 212. Date of bud break Pink bud Full bloom Fruitlet 14-Mar 4-Apr 11-Apr 23-May Anita 14-Mar 4-Apr 11-Apr 23-May 14-Mar 4-Apr 18-Apr 23-May 14-Mar 28-Mar 11-Apr 23-May 14-Mar 28-Mar 11-Apr 23-May 14-Mar 28-Mar 11-Apr 23-May 14-Mar 4-Apr 11-Apr 23-May Harvest date The order in which each cultivar was ready to be picked followed the same pattern in each of the three years as shown in Table 7 and the consistency in these results bodes well for the establishment of the new cultivars. had a similar picking date to that of in 21, but in 211 started cropping a week earlier than. This would potentially make useful by offering another early cultivar for the start of the U.K. plum season. was the latest cultivar, cropping at about the same time as Marjorie s Seedling on farms in the Faversham area. This may present another option for this late cropping period, particularly as fruit size, yield and fruit flavour all scored well in this trial. and were both harvested between and, which may prove useful for this four week period where no suitable alternatives exist currently. Anita and cropped in the period between and. For, its fruit quality may prove to be too poor to be commercially acceptable, but Anita, particularly because of its large fruit size, may fill this gap with fruit of an acceptable quality. 26

30 Table 7. The date of first pick for each cultivar from 21 to 212. Picking sequence is also given with the earliest cultivar assigned order 1 and the latest cultivar order 7. Cropping Cropping Cropping 21 Sequence 211 Sequence 212 Sequence 5-Aug 1 13-Jul 1-5-Aug 1 2-Jul 2 1-Aug 1 Anita 9-Aug 2 25-Jul 3 9-Aug 2 17-Aug 3 25-Jul 3 2-Aug 3 25-Aug 4 15-Aug 4 3-Aug 4 7-Sep 5 17-Aug 5 8-Sep 5 1-Sep 6 29-Aug 6 16-Sep 6 15-Sep 7 6-Sep 7 19-sep 7 27

31 Cultivar summaries Images and the attributes of each of the cultivars trialled are presented in the following pages Anita Summary of attributes Anita produced the largest fruit size of any cultivar in this trial. It is relatively early, with harvest starting up to eight days after and other than, it was the only cultivar with harvest occurring between and. However, its flavour was not exceptional with fruit having maximum total soluble solids of 18 Brix. It is a very large purple plum which, whilst not striking, does offer something different to the current range of standard cultivars being grown in the UK and so, whilst not the cultivar with the best fruit quality, it did have attributes which may make it suitable for trialling commercially. 28

32 Summary of Attributes had by far the best flavour of any plum tested in this trial. Whilst formal taste panel assessment was not within the remit of the project, it was sampled by a number of growers and retailers and was well regarded. It had very high total soluble solids, which was the highest of any cultivar tested at generally around 25 Brix. Its appearance will not make it stand out to consumers though as it is not as large as Anita and is simply a small round purple plum. Cracking and general skin finish were issues in 21 and 212, however fruit quality was much improved in 211, presumably a factor of the weather. Its skin finish is an issue though and in a year where the weather is not optimum, this would result in a large percentage of fruit being graded non-marketable. Yields were low in both 21 and 212 but actually one of the highest of the new cultivars in 211. This is perhaps its main negative attribute as this bienniality would need to be addressed before it could be considered for commercial production on any scale. 29

33 Summary of attributes is a very late cultivar with harvest starting around the same time as Marjorie s Seedling. The yield was consistently one of the highest of all the new cultivars under trial here. Fruit size is good and the flavour, whilst not as good as, also achieved a total soluble solids of up to 25 Brix. Since this project started, has been planted by growers in larger commercial trial blocks and seems to be performing well. 3

34 Summary of attributes was the earliest new cultivar in this trial with harvest starting at the same time as or just before. has a very similar taste and appearance to, which suggests that consumers would find it acceptable. Size is good but yield was one of the lowest of the new cultivars, particularly in 212 when no fruit was produced at all. Brix and taste are reasonable, achieving a Brix of up to 2. As an alternative to at the start of the season, it may prove suitable. 31

35 Summary of attributes was a very dry plum with poor flavour and flesh which did not contain any juice. Whilst size is good, its flavour would make this unacceptable. Yield was also low. 32

36 Summary of Attributes is very similar to, both in the appearance of the fruit and the trees. The fruit size was good but flavour was not exceptional. Because it is earlier than by a few days, or up to a week, it could form part of a longer cropping profile including the two cultivars, but of the two seems to have more positive attributes. Flavour of was generally accepted to be better than. 33

37 Conclusions After four years of fruiting, the consistent findings regarding the new cultivars confirm their characteristics and their potential for commercial cultivation. Anita,, and all show promise as new cultivars for commercial production. For, the combination of consistent yield, late timing and fruit quality probably make it the most likely cultivar for commercial uptake and it would certainly be worth growers considering a trial area. Cropping at about the same time as Marjorie s Seedling it does offer an alternative as a late cultivar at the end of the season., however, was an early cultivar and was harvested at approximately the same time as, or even up to a week earlier, as was the case in 211. had similar fruit characteristics to which may make it an attractive cultivar, however did not yield particularly well and seemed to be the most sensitive to adverse weather whereby in 212, no fruit were produced at all. Whilst Anita showed promise for its good fruit size and yield, its taste was not exceptional. produced fruit with an excellent flavour but had issues with skin finish and inconsistent yields. Anita and may be suitable for commercial trials but issues with the yield of in particular would need to be addressed for it to be suitable for commercial production. was not suitable for commercial production and whilst did have certain positive attributes, the fact that it cropped at such a similar time to makes it unlikely to find a place commercially. Technology Transfer FAST Annual Stone Fruit Conference Presentation, December 21 HDC News article, submitted March 211 A grower s field walk was held at the trial site in September 211 to offer the industry a chance to view the new cultivars. Results from 21 and 211 were presented at the annual Marks and Spencer plum growers meeting on 1 December

38 References Hartmann, W. (1998). New plum cultivars from Hohenheim. Proceedings of the VI International Symposium on Plum, Prune Genetics and Breeding. Acta Horticulturae, 478, Hartmann, W. and Petruschke, M. (2). Sharka resistant plums and prunes by utilisation of hypersensitivity. Acta Horticulturae, 538, Ogasanovic, D. (1991). A new dessert plum cultivar. Acta Horticulture, 283, Renaud, R. and B. Lafargue (1998). : A new European plum cultivar. Proceedings of the VI International Symposium on Plum, Prune Genetics and Breeding. Acta Horticulturae, 478, Sudar, R., Jurkovic, Z., Dugalic, K., Tomac, I., Viljevac, M. and Jurkovic, V. (211). Sorbitol and sugar composition of plum fruit during ripening. Proceedings of the 46th Croatian and 6th International Symposium on Agriculture, Opatija, Croatia,