Pollination Requirements of Japanese Plum (Prunus salicina) Cultivars JANNIE DE KLERK & CHRIS SMITH

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Pollination Requirements of Japanese Plum (Prunus salicina) Cultivars JANNIE DE KLERK & CHRIS SMITH SUMMARY Pollination must first take place before fruit can develop.

1 Pollination Requirements of Japanese Plum (Prunus salicina) Cultivars JANNIE DE KLERK & CHRIS SMITH SUMMARY Pollination must first take place before fruit can develop. Most of the Japanese plum cultivars are self-incompatible. For adequate pollination to take place it is very important to plant suitable cross pollinators in the correct ratio of cultivar to pollinator to ensure an economically viable fruit set. Data from the ARC s Bien Donné Research Farm as well as commercial farms are presented to indicate which cross-pollinators and ratios are required for most commercially grown Japanese plum cultivars planted in early and late maturing areas. At least 10% of the blossoms of the trees must be open before bee hives are moved into the orchard. Most pesticides are toxic to bees and should not be sprayed in the orchard during flowering time. The effective pollination period (EPP) influences fruit production and is a useful parameter to analyse and detect factors limiting fruit set. INTRODUCTION The release of a new Japanese plum variety to the fruit industry raises questions regarding the pollination requirements of the variety. Is it self-pollinating or does it require a cross-pollinator to help ensure a good fruit set of quality fruit? If the variety needs a cross-pollinator, which one will be the most suitable? In what ratio must trees of the variety and the crosspollinator be planted? These questions, the biology of fruit set, as well as the role of honey bees in the pollination process of Japanese plum cultivars, will be discussed in this article. style and a two-lobed stigma (female part of the flower). Only one of the two ovules usually develops. Stamens are longer, shorter, or the same length as the stigma depending on the variety. The stigma is receptive as soon as the flower opens and the flower stays fully open for three to five days. Flowers in a tree and between trees in an orchard can flower over a period of time depending on the climate and environmental conditions. Anthers usually release pollen only after the flower is fully open. The flowers will soon drop from the tree if they are not pollinated. Apart from the absence of sufficient bee activities during the EPP, unfavourable weather conditions like low temperatures, rainfall and strong wind, have an adverse effect on set and optimum fruit production. COMPATIBILITY In order for fruit to develop, pollination must first take place during the flowering season. Pollination is the transfer of pollen from the anther of a flower to the stigma of the same flower, or other flowers on the same tree, or flowers on a tree of a different variety resulting in fertilisation. Some plum cultivars are pollinated with their own pollen and are therefore classified as self-compatible (self-pollinating). For the release of new plum cultivars, the detection of the S- alleles (genes that prevent self-pollination) has become important in order to determine the most suitable cross-pollinator for a particular cultivar in a specific climatic zone. Most of the Japanese plum cultivars require viable pollen from a different Japanese plum variety to be pollinated (cross-pollination) and are therefore self-incompatible. Cross pollinator(s) for a specific plum variety may differ in the flowering period between areas due to environmental differences, affected by the specific chilling and heat requirements of cultivars. A self-incompatible variety and its cross-pollinator(s) should flower at more or less the same time in order for FLOWERS Flowers of the Japanese plum (Prunus salicina) variety are each about 2.5 cm wide and consists of five petals, several stamens with anthers (male part of the flower), a one compartment ovary (two ovules inside) with a Figure 1: Artificial pollination of two plum trees in an enclosed structure. TECHNOLOGY 57 OCT NOV 2013

Figure 2: Development of fruit on the plum tree after successful pollination.

The ideal situation would be for the donor variety to start blossoming prior to the receiving variety in

Figure 3: Excessive fruit on the plum trees after pollination are harvested, counted and weighed.

absent, resulting in financial losses to the producer.

can be rectified by planting the correct cross pollinator for a specific area in a recommended ratio.

must be used and in what ratio must trees of the variety and the cross-pollinator be planted.

but also planting the correct ratio of cultivar to pollinator to ensure an economically viable fruit set.

To determine the planting ratio for a new cultivar, the total fruit set (number of fruit thinned to

2 Figure 2: Development of fruit on the plum tree after successful pollination. cross-pollination to take place and to ensure good fruit set. The ideal situation would be for the donor variety to start blossoming prior to the receiving variety in order to pollinate the early blossoms which normally provide the better fruit. Figure 3: Excessive fruit on the plum trees after pollination are harvested, counted and weighed. PLANTING RATIO Without adequate pollination, the fruit set of a plum variety may be insignificant or even absent, resulting in financial losses to the producer. This is, however, not necessarily an indication of the yield potential of the variety and in most cases can be rectified by planting the correct cross pollinator for a specific area in a recommended ratio. The two questions in respect of a self-incompatible Japanese plum variety are: which cross-pollinator must be used and in what ratio must trees of the variety and the cross-pollinator be planted. It is essential that producers realise the importance of planting not only suitable cross pollinators, but also planting the correct ratio of cultivar to pollinator to ensure an economically viable fruit set. This can also differ geographically as previously indicated. To determine the planting ratio for a new cultivar, the total fruit set (number of fruit thinned to commercial standard plus the number of fruit harvested) under controlled DS DRING AAN OP DIE BESTE, DRING AAN OP DS METSON is deel van CropLife Groei Saam met Ons; Metson! South Africa Suid-Afrika M W MetsonWorld DESKUNDIGES IN PLANTVOEDING, BYMIDDELS, NATUURLIKE GROEISTIMULANTE EN GEWAS GESONDHEID TEGNOLOGIE 58 OKT NOV 2013

3 Table 1. Update of the general cross-pollination chart regarding the different commercial Japanese plum cultivars planted in South Africa. Cultivar Cross-Pollinators for Cross-Pollinators for Ratio ** Early Maturing Areas (<600 ICU*) Late Maturing Areas (>600 ICU*) African Delight TM Pioneer Pioneer 1:10 African Rose Self-compatible Self-compatible - Angeleno Sapphire, Harry Pickstone, Pioneer, Fortune Santa Rosa, Souvenir, Larry Anne, Laetitia, Gaviota 1:8 Casselman Self-compatible Self-compatible - Early Santa Rosa Self-compatible Self-compatible - Flavorking Sapphire, Harry Pickstone, Santa Rosa Laetitia, Songold 1:12 Flavorich Harry Pickstone Sapphire, Fortune 1:12 Flavor Queen Harry Pickstone Sapphire, Ruby Red 1:12 Fortune Harry Pickstone, Angeleno, Souvenir 2 Souvenir 2, Santa Rosa, Angeleno, Lady Red 1:12 Gavearli Santa Rosa Santa Rosa 1:12 Gaviota Santa Rosa Santa Rosa 1:12 Golden Kiss Sapphire, Angeleno Sapphire, Angeleno 1:12 Harry Pickstone Self-compatible Self-compatible - Lady Red Laetitia, Songold Songold, Laetitia 1:12 Lady West Sapphire, Laetitia Laetitia 1:12 Laetitia Songold, Lady Red Songold, Casselman 1:12 Larry Anne Songold, Laetitia Songold, Angeleno, Santa Rosa 1:12 Pioneer Self-compatible Self-compatible - Reubennel Self-compatible Self-compatible - Purple Majesty Harry Pickstone, Sun Kiss Sun Kiss, Laetitia 1:12 Ruby Red Sapphire, Souvenir, Laetitia Songold, Laetitia 1:12 Ruby Star Self-compatible Self-compatible - Santa Rosa Self-compatible Self-compatible - Sapphire Harry Pickstone, Fortune, Angeleno Harry Pickstone, Souvenir, Sun Kiss 1:12 Songold Laetitia, Ruby Red, Lady Red Laetitia, Ruby Red 1:12 Southern Belle Songold, Laetitia Songold, Laetitia - Souvenir Sapphire, Harry Pickstone Santa Rosa 1:12 Sun Breeze Sapphire, Laetitia, Ruby Red Laetitia, Ruby Red, Sun Kiss 1:12 Sun Kiss Harry Pickstone, Sundew, Sapphire Laetitia, Sundew, Sapphire 1:12 Sundew Harry Pickstone, Sundew, Sapphire Laetitia, Sun Kiss 1:12 Sunset Songold Larry Anne 1:12 Sun Supreme Sun Breeze, Sun Kiss, Golden Kiss, Songold Golden Kiss, Laetitia, Reubennnel 1:12 Sensation Self-compatible Self-compatible - * ICU = Infruitec Chilling Units. ** = Cross-pollinator to Cultivar ratio. conditions as well as the percentage fruit thinned, must be calculated. This calculation is usually done by artificial cross- or self-pollination of two trees by honey bees by isolating the two trees from foreign pollen in an enclosed structure (Figure 1, 2 and 3). Cross- and self-pollination trials are routine- ly conducted annually at Bien Donné Research Farm (Simondium area) in the Western Cape on all promising newly bred ARC Japanese plum cultivars and the results are summarized in Table 1. This tabulation of pollination data is an ongoing process which is supported by field observations in the industry on farm level. POLLINATION BY HONEY BEES Honey bees are an important vector for pollinating plum trees in South Africa. The fact that honey bees are not attracted to the blossoms of certain plum cultivars creates a major problem for producers. Bees prefer to forage in the flowers of other plant species TECHNOLOGY 59 OCT NOV 2013

before turning to the flowers of plum trees. If possible, any competing flowering plants in the plum orchard should be eliminated in order for the bees to concentrate on the flowers of the plum trees.

This is to keep the bees working in the flowers of the plum trees and not lured away by more attractive flowers of plants nearby.

Bees work best when temperatures are above 18ºC, wind speed is lower than 38 km/h and if there is more than 60% full sunlight.

4 before turning to the flowers of plum trees. If possible, any competing flowering plants in the plum orchard should be eliminated in order for the bees to concentrate on the flowers of the plum trees. At least 10% of the blossoms of the trees must be open before bees are moved into the orchard. This is to keep the bees working in the flowers of the plum trees and not lured away by more attractive flowers of plants nearby. Plum flowers are the most receptive to pollination as soon as they have opened. Under cool, moist conditions, plum flowers may not be the most receptive until 24 hours after opening. Bees work best when temperatures are above 18ºC, wind speed is lower than 38 km/h and if there is more than 60% full sunlight. Cool weather, rain or wind may prevent bees from leaving their hives, and reduces pollen tube growth which in turn reduces fertilization and fruit set. Unfavourable weather conditions during the pollination period are a problem that producers have to contend with. Most pesticides are toxic to bees and should not be sprayed in the orchard during flowering time. EFFECTIVE POLLINATION PERIOD The effective pollination period (EPP) concept was developed by Williams (1965) and is defined as the number of days during which pollination is effective in producing fruit (interval of time during which fertilization can occur). This is determined by the longevity of the ovules minus the time lag between pollination and fertilization. EPP plays a clear role controlling cropping in fruit trees and is a useful parameter to analyse and detect factors limiting fruit set. It is influenced by three main processes: stigmatic receptivity, pollen tube growth rate and ovule longevity. These three processes are in turn influenced by temperature, flower quality and chemical treatments. S ALLELE The S-allele or self-sterility genes are genes that prevent self-pollination in flowering plants. This is a genetic phenomenon breeders have to deal with in order to secure a good pollination ratio for all new cultivars. S- alleles control the growth CONTINUED ON PAGE 62 TEGNOLOGIE 60 OKT NOV 2013

5 Commercial Banking Growth comes easy with our financing solutions for your farming business. MetropolitanRepublic/12016/E t FNB, we understand the nature of farming, and that you are constantly looking for opportunities to grow your business. An FNB AExpansion Loan is a customised medium to long-term loan that can help you establish or expand your agricultural production. This loan is perfect for financing infrastructure with a productive lifespan longer than a year, such as facilities required for dairy farming and broiler production, or to finance expansion that won t yield immediate returns for instance establishing fruit orchards, vineyards, or timber plantations. If you are an established farmer, or have proven financial track records and additional farmland and water rights available, this loan offers you the following benefits: There is NO limit to the amount you can apply for, as your loan is tailormade to suit your business specific needs. The facility is determined by analysing your needs, the viability of the farming venture, the source of repayment, and the amount and type of security offered. Your repayment term will be determined by the farming enterprise and the economic lifespan of the production facilities, but it is usually between 5 and 10 years. You can structure your repayment to suit your business cash flow pay interest and capital monthly, or alternatively pay interest monthly but capital quarterly, half-yearly or annually. You also have the option of suspending your capital repayment for a period up to 2 years, should your orchards or vineyards with newly planted trees and vines only be in full production after 3 to 5 years. Interest rates are based on your risk profile, securities offered, and are linked to the South African Reserve Bank prime interest rate. When applying for this loan, it will help to follow these general guidelines: You will have to give convincing evidence that you will be able to repay the loan out of your farming proceeds or from other sources of income, by way of a cash flow projection if it is an existing farming operation or a business plan if it is a new farming venture. This cash flow projection must indicate seasonal, regular and irregular income, foreseen and unforeseen expenses, and withdrawals for living expenses. Budgets and cash flow forecasts are required to support the loan, work out the maximum amount required and demonstrate affordability. Your balance sheet will have to show adequate net assets to offer sufficient security in the event that your farming business should fail. This is to ensure that our depositors whose money has been lent to you is not lost. In most cases, a mortgage bond will be taken over the farm property, equal to our realistic valuation thereof. Other security may include notarial bonds and suretyships. You will have to show that you have sufficient knowledge, skill and experience to manage the farming business to achieve the financial results that you indicated in your cash flow projections. This includes the fulfilment of past contracts and proof of historical yields and sales. To apply for an FNB Expansion Loan, talk to an FNB Commercial Banker at your nearest FNB branch. Your Commercial Banker will conduct an analysis of your specific needs and provide a suitable solution tailored for your business. You will be quoted a competitive rate, given flexible repayment options and receive an answer on your loan application through a transparent process. If your farming business is going far, we can help you get there. For more information on FNB s agriculture solutions, visit your nearest branch or contact your Commercial Banker. You can also agric@fnb.co.za or visit This article is for information purposes only and does not replace or compromise any of the bank s credit policy or conditions applicable to agricultural loans. Terms and conditions apply. First National Bank a division of FirstRand Bank Limited. An Authorised Financial TECHNOLOGY Services and Credit Provider OCT (NCRCP20). NOV

CONTINUED FROM PAGE 60 of the pollen tube, thus causing male sterility and governing compatibility relationships. Molecular methods to detect these S-alleles are becoming increasingly available.

6 CONTINUED FROM PAGE 60 of the pollen tube, thus causing male sterility and governing compatibility relationships. Molecular methods to detect these S-alleles are becoming increasingly available. This would be helpful to predict compatibility relationships in Japanese plum cultivars and needs further investigation. CONCLUSION For the fruit farmer, it is important that there should be the optimum number of fruit on the tree at harvest time. Besides other factors, optimal fruit production is obtained with the correct pruning method as well as proper thinning of flowers and/or fruit. To obtain a good fruit production with most of the Japanese plum cultivars, sufficient pollination in addition to above mentioned factors, must occur. Therefore it is important to plant the correct cross-pollinator in the correct ratio to the cultivar. Ideal conditions for the bees should prevail to ensure that it can work optimally and that adequate pollination can take place. There are a number of factors that influence the production of Japanese plums. If one of these factors is absent or not optimal, fruit production will be adversely affected. ACKNOWLEDGEMENTS Sincere thanks to SASPA for partial funding of the research project, Mike Allsopp of the Plant Protection Research Institute of the ARC for essential advice, as well as supplying the bees and beekeeping equipment, and Pieter Quixley, farm manager at Bien Donné Research Farm (ARC Infruitec-Nietvoorbij) for handling the bees. REFERENCES Williams, R.R. (1965). The effect of summer nitrogen applications on the quality of apple blossoms. J. Hort. Sci. 40: TEGNOLOGIE 62 OKT NOV 2013

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