Abstract
Parthenocarpic fruit development (PFD) reduces fruit yield and quality in grapevine. Parthenocarpic seedless berries arise from fruit set without effective fertilization due to defective pollen germination. PFD has been associated to micronutrient deficiency but the relation of this phenomenon with pollen polymorphism has not been reported before. In this work, six grapevine cultivars with different tendency for PFD and grown under micronutrient-sufficient conditions were analyzed to determine pollen structure and germination capability as well as PFD rates. Wide variation in non-germinative abnormal pollen was detected either among cultivars as well as for the same cultivar in different growing seasons. A straight correlation with PFD rates was found (R2 = 0.9896), suggesting that natural parthenocarpy is related to defective pollen development. Such relation was not observed when PFD was analyzed in grapevine plants exposed to exogenous gibberellin (GA) or abscissic acid (ABA) applications at pre-anthesis. Increase (GA treatment) or reduction (ABA treatment) in PFD rates without significative changes in abnormal pollen was determined. Although these plants were maintained at sufficient boron (B) condition, a down-regulation of the floral genes VvBOR3 and VvBOR4 together with a reduction of floral B content in GA-treated plants was established. These results suggest that impairment in B mobility to reproductive tissues and restriction of pollen tube growth could be involved in the GA-induced parthenocarpy.
Highlights
Grapevine is one of the most cultivated and economically important fruit crop worldwide
Results suggest that while impairment in pollen development and the incidence of abnormal pollen could be the main cause of parthenocarpy under field-growing conditions, variation in Parthenocarpic fruit development (PFD) rates observed in GA and abscissic acid (ABA) exposed plants seems to be related to changes in transporter-mediated B mobility to floral tissues
The occurrence of morphologically abnormal pollen has been observed in other grapevines cultivars like Loureiro, Mourisco, Picolit Giallo, Moscato Rosa, Ceresa and Bicane, all of which are characterized by their low fruit productivity [30,31,32]
Summary
Grapevine is one of the most cultivated and economically important fruit crop worldwide. Foliar applications of B and Zn to maintain adequate micronutrient concentrations is a common vineyard management practice [17,18].variable PFD rates are still detected after these treatments, suggesting that causes other than micronutrient deficiency are originating this phenomenon In this sense, since changes in endogenous levels of GA, ABA and auxins after pollination are determining factors for fruit setting and initiation [19,20], hormonal causes for PFD have been invoked. Fruit set occurs even without pollination by inducing the expression of genes associated to GA and auxin biosynthesis [20] Supporting this assumption, exogenous GA application to inflorescences at pre-bloom stage can induce fruit set without effective fertilization, leading to a PFD in different grapevine cultivars [19,21,22,23]. Results suggest that while impairment in pollen development and the incidence of abnormal pollen could be the main cause of parthenocarpy under field-growing conditions, variation in PFD rates observed in GA and ABA exposed plants seems to be related to changes in transporter-mediated B mobility to floral tissues
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