Determination of Potential Pollinizer Grafted Pear Hybrids (Pyrus communis × Pyrus pyrifolia) for Subtropical Regions in Brazil

Abstract

The pear tree is originally a temperate-climate fruit tree. The cross Pyrus communis × Pyrus pyrifolia generated hybrid cultivars adapted to subtropical regions. However, the low effective fruiting is a limiting factor for the expansion of pear tree crops in subtropical regions and no pollinizer plants have been identified for these cultivars in subtropical regions. This work aimed to identify possible pollinizer pear tree cultivars in subtropical regions by evaluating the stigmatic receptivity, the germination percentage, and the number of pollen grains. Seven hybrid pear cultivars were used. Flowers of each cultivar at each floral stage were collected (E, E2, F, F2, and G). The stigmatic receptivity was evaluated by immersing the material in 3% hydrogen peroxide. Flowers were collected for the quantification of anthers, pollen grains per anther and per flower, and pollen grain germination. Stigmas were 100% receptive for all cultivars at the F2 and G stages. Cultivar Cascatense showed a large number of anthers and pollen grains per anther and per flower. The highest pollen grain germination percentage was detected for Cascatense (72.75%). Cultivars Seleta and Triunfo have high stigmatic receptivity for a longer period during the flowering stage, proven to be a potential female parent. Cascatense has a higher germination percentage and a larger number of anthers per flower, pollen grains per anther, and pollen grains per flower. Cascatense has a high potential to be used as a pollinizer, both in pear tree breeding programs and commercial orchards.

Selection of pollinator cultivars for pear trees in a subtropical climate

“…This result demonstrates that controlled crosses of these cultivars can be performed before the opening of the flower in genetic improvement programs. However, Bisi et al (2019b) found a shorter period of stigmatic receptivity than done here, which may be due to the high temperatures reported by those authors. Stigmatic receptivity is a key factor in the assessment of compatibility between cultivars, as the suitability of flowers in the fertilization process is directly related to their receptivity to pollen grain (Zambon et al 2018).…”

“…All stages of reproductive development showed the formation of bubbles in the stigma cavity when subjected to the 3% hydrogen peroxide test, indicating the activity of the peroxidase enzyme. Bisi et al (2019b) observed 100% receptivity in the stages after floral anthesis and in the balloon stage (preanthesis) in the cultivars 'Seleta' , 'Tenra' , and 'Triunfo' . This result demonstrates that controlled crosses of these cultivars can be performed before the opening of the flower in genetic improvement programs.…”

“…Despite the morphological similarities of the androecium, several studies show that the amount and viability of pollen in pear flowers can vary greatly between species and cultivars (Nogueira et al 2016). Bisi et al (2019b) stated that these variations in pollen quantity and viability may be related to characteristics inherited from their progenitors and/or may be associated with the adaptation of cultivars to the environment where they live.…”

“…The stigmatic receptivity was verified by the viscous and wet aspect of the stigma and tested by adding 3% hydrogen peroxide (H 2 O 2 ) to detect the action of the peroxidase enzyme, whose presence was indicated by the formation of small bubbles in receptive stigmas (Bisi et al 2019b).…”

“…Low fruiting is related to the pollination process. The absence of fertilization of the ovule in pear flowers results in fewer fruits and causes reduction in production (Bisi et al 2019b).…”