Reproductive compatibility and diallel analysisamong pear trees in the tropics

Abstract

In recent decades, there has been increasing exploitation of pear (Pyrus ssp.) in subtropical and tropical regions. However, the low fruit set due to gametophytic incompatibility and the excision of cultivars adapted to these climatic conditions, are limiting factors in the expansion of the pear tree in these regions. In order to assist the selection of parents in breeding programs for pear tree breeding and the selection of pollinator cultivars in orchard planning in subtropical and tropical regions, three studies were conducted. In the first study, the objective was to identify the possible pollinators for pear cultivars in subtropical regions, through the evaluation of the stigmatic receptivity, the percentage of pollen grain germination and the number of pollen grains per anther and flower of hybrid pear tree cultivars, Cascatense, Centenária, D’água e Primorosa, Seleta, Tenra e Triunfo. In the second study, the molecular characterization of the S-alleles of pear tree cultivars was carried out and the fruit set from the cross pollination among these cultivars under field conditions was evaluated. The S-alleles of the seven cultivars were characterized by PCR and under field conditions were self-pollination, parthenocarpy and cross-pollination among these cultivars. In the third one, the general (GCA) and specific (SCA) combining ability in diallel crosses to assist in the selection of pollenizers in hybrid pear tree cultivars (Pyrus communis x Pyrus pyrifolia) adapted to the subtropical climate. Diallel analysis was performed, following the Griffing model 1 method to estimate the GCA, SCA and ER from the parents, F1 hybrids and reciprocal F1 hybrids obtained from the self-pollination and crossings between Cascatense, Centenária, D 'água and Primorosa. The cultivars Seleta and Triunfo have potential as female genitors. The cultivar Cascatense and Primorosa have high potential to be used as pollinators. The S-alleles identified in this study are: Cascatense - S1S5, Centenaria - S5, D’água - S5S8, Primorosa - S1S5, Seleta - S1S4, Tenra - S5 and Triunfo -S1S5. The cultivars D'água and Seleta are compatible. However, they have no potential as pollinators. The cultivars Primorosa, Cascatense and Triunfo have incompatibility. Centenaria has a greater general combining ability with Cascatense, D'Agua and Primorosa cultivars. The Primorosa x Centenaria cross has the highest specific combining ability, conferring Centenaria a great pollinator for the cultivar Primorosa in relation to the physicochemical qualities of the fruits.