Parthenocarpy and Self-Incompatibility in Mandarins

Rafael Montalt,Pablo Aleza,Patrick Ollitrault,Luis Navarro,María Carmen Vives

doi:10.3390/agronomy11102023

Abstract

Citrus reproductive biology is complex. One of its characteristic features is parthenocarpy that enables seedless fruit production. Citrus parthenocarpy and self-incompatibility knowledge is only partial and sometimes discrepant. Increasing such knowledge is relevant for better managing cultivated varieties and improving the selection of parents in breeding strategies to recover seedless varieties such as mandarins. This work develops an efficient protocol to characterize self-incompatibility and different parthenocarpy types based on emasculation, hand self-pollination, and hand cross-pollination. It analyzes fruit setting and seed production coupled with histological pollen performance observations. We analyzed the reproductive behavior of nine mandarin varieties with relevant characteristics as parents for seedless mandarin breeding. ‘Clemenules’ clementine and ‘Moncada’ mandarins were strictly self-incompatible with facultative and vegetative parthenocarpy; ‘Imperial’ mandarin and ‘Ellendale’ tangor displayed no strict self-incompatibility associated with facultative and vegetative parthenocarpy; ‘Fortune’ mandarin was self-incompatible with facultative and stimulative parthenocarpy; ‘Campeona’ and ‘Salteñita’ mandarins were self-compatible with vegetative parthenocarpy; ‘Serafines’ satsuma was associated with male sterility together with facultative and vegetative parthenocarpy; and ‘Monreal’ clementine was self-compatible and nonparthenocarpic. Our protocol can be applied for screening of mandarin germplasm and to characterize new parents. Reproductive behavior knowledge is important for optimizing seedless mandarin breeding programs based on diploidy, triploidy, or induced mutagenesis.

Highlights

Seedlessness is one of the most important characteristics for citrus fresh-fruit markets because consumers do not accept seedy fruit
We assessed if the studied varieties had parthenocarpic ability (PA) and if a pollination stimulus was required for seedless fruit to set
Parthenocarpic ability is a key reproductive biology component because it enables seedless fruit production when combined with other reproductive features such as male and female sterility or self-incompatibility

Summary

Introduction

Seedlessness is one of the most important characteristics for citrus fresh-fruit markets because consumers do not accept seedy fruit. Stenospermocarpy is uncommon [4] and ovule sterility or lack of its fecundation (self-incompatibility or no compatible viable pollen) coupled with parthenocarpy is necessary for the production of seedless fruits. Lack of fecundation, or no seed development at early stages often prevents seed formation and different mechanisms have been reported in citrus [2,5]. Ovule sterility can be originated in flowers whose pistils do not develop up to the functional stage [6]. Osawa [7] observed degeneration of the embryo sac in both navel sweet orange (C. sinensis (L.) Osbeck) and satsuma mandarin (C. unshiu (Mak.) Marc.) and Wong [8] reported chromosome aberrations into the embryo sac as the responsible mechanism of low seed number in hand-pollinated flowers of ‘Valencia’

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Conclusion