In this work, 75 avocado accessions maintained in an ex situ germplasm collection at the E.E. la Mayora in Málaga (Spain) were characterized with 16 microsatellites previously developed in this species. This avocado collection includes both local Spanish genotypes obtained through prospection and genotypes obtained by exchange with different countries. A total of 156 different amplification fragments were detected ranging from 4 to 16 per locus with an average of 9.75 alleles per locus. All the microsatellites were highly informative with an expected heterozygosity higher than 0.5 and a probability of identity below 0.36. The total probability of identity was 2.85x10(-14). Fifteen of the 16 loci studied showed a positive Wright's fixation index (F) indicating a deficit of heterozygotes with an average over all the SSRs of 0.18. A dendrogram was generated using UPGMA (unweighted pair group method with arithmetic averages) based on the Nei and Li similarity index. This dendrogram classified most of the genotypes analyzed into three major groups which mainly differed in racial origin although with low bootstrap support probably due to the presence of many interracial hybrids in the collection. All the genotypes studied could be unequivocally distinguished with the combination of SSRs used except some putative mutations of 'Hass' and an additional group of two cultivars. The results obtained indicate that the set of SSRs used is highly informative and are discussed in terms of their implications for avocado germplasm characterization and management.

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A common observation in different plant species is a massive abscission of flowers and fruitlets even after adequate pollination, but little is known as to the reason for this drop. Previous research has shown the importance of nutritive reserves accumulated in the flower on fertilization success and initial fruit development but direct evidence has been elusive. Avocado (Persea americana) is an extreme case of a species with a very low fruit to flower ratio. In this work, the implications of starch content in the avocado flower on the subsequent fruit set are explored. Firstly, starch content in individual ovaries was analysed from two populations of flowers with a different fruit set capacity showing that the flowers from the population that resulted in a higher percentage of fruit set contained significantly more starch. Secondly, in a different set of flowers, the style of each flower was excised one day after pollination, once the pollen tubes had reached the base of the style, and individually fixed for starch content analysis under the microscope once the fate of its corresponding ovary (that remained in the tree) was known. A high variability in starch content in the style was found among flowers, with some flowers having starch content up to 1,000 times higher than others, and the flowers that successfully developed into fruits presented significantly higher starch content in the style at anthesis than those that abscised. The relationship between starch content in the ovary and the capacity of set of the flower together with the correlation found between the starch content in the style and the fate of the ovary support the hypothesis that the carbohydrate reserves accumulated in the flower at anthesis are related to subsequent abscission or retention of the developing fruit.

In avocado, only a very small fraction of the flowers are able to set fruit. Previous work in other woody perennial plant species has shown the importance of carbohydrates accumulated in the flower in the reproductive process. Thus, in order to explore the implications of the nutritive status of the flower in the reproductive process in avocado, the starch content in the pistil has been examined in individual pollinated and non-pollinated flowers at anthesis and during the days following anthesis. Starch content in different pistilar tissues in each flower was quantified with the help of an image analysis system attached to a microscope. Flowers at anthesis were rich in highly compartmentalized starch. Although no external morphological differences could be observed among flowers, the starch content varied widely at flower opening. Starch content in the ovary is largely independent of flower size because these differences were not correlated with ovary size. Differences in the progress of starch accumulation within the ovule integuments between pollinated and non-pollinated flowers occurred concomitantly with the triggering of the progamic phase. The results suggest that starch reserves in the ovary could play a significant role in the reproductive process in avocado.