Viability and receptivity of reproductive structures in Lima bean (Phaseolus lunatus L.) for improvement programs

Abstract

Artificial hybridization in Phaseolus lunatus L. is still little used in genetic improvement programs in Brazil due to the low establishment percentages. This work aimed to evaluate pollen viability and stigma receptivity in different Lima bean genotypes throughout the day. Accessions 'Roxinha -MT' and 'Cana Longa-PB' were used in the experiment. Five flower buds were collected from each genotype at 6:00 a.m., 10:00 a.m., 2:00 p.m., and 6:00 p.m. The stigma receptivity was determined using 3% hydrogen peroxide, whereas pollen viability was determined with 2% acetocarmine colouration. The genotype and time factors acted independently on the percentage of viable and non-viable pollen grains and stigma receptivity. The genotype 'Roxinha' presented 88.54% viable pollen grains, a value 84.27% higher than that of the 'Cana Longa' genotype. This percentage varied as a function of time, with the highest means observed at 6:00 a.m. Stigma receptivity was influenced only by the time of the day, undergoing a great reduction in receptivity, from 88% in the early morning to slightly more than 40% around noon. These results indicate that 6:00 a.m. is the most suitable time to perform artificial crosses in Lima bean plants.