Pollen viability and incompatibility in indigenous rice bean (Vigna umbellata (Thunb.) Ohwi & Ohashi)

Pollen viability, germination and compatibility are essential in determining the success of pollination and seed setting of high-valued crops. Rice bean (Vigna umbellata (Thunb.) Ohwi & Ohashi) is an underutilized and unexplored indigenous legume with high potential for commercial production. In this study, pollen quality, viability, germination rate and incompatibility among selected six rice bean (V. umbellata) accessions from Barili, Cebu, Philippines were evaluated to determine the barriers and effective pollination habit for increased productivity while retaining the important traits, including high tolerance in poor soils, superior climatic resilience and resistance to pest and diseases. Results of acetocarmine calorimetric assay showed that rice beans' (V. umbellata) pollens are highly viable, with accessions VU 004 (56.33 +/- 4.91%) and VU 007 (54.34 +/- 4.53%) having the optimum viability rate. Brewbaker and Kwack medium treated with 0.2 g.l(-1) and 0.3 g.l(-1) boric acid (H3BO4) enhanced the germination rate in vitro (11.56 +/- 5.53% and 9.47 +/- 6.50% respectively). Bud (14.96 +/- 1.53%) and post-anthesis pollens (10.28 +/- 0.94%) have optimum germination rate in 0.2 g.l(-1) boric acid media, while anthesis pollens are suitable in media supplemented with sucrose and boric acid alone (12.20 +/- 1.50%) and with 0.1 g.l(-1) myo-inositol supplementation (8.49 +/- 1.86%). Pollination test revealed that rice bean accessions have high self-compatibility (50.76 + 3.45%) and low cross-compatibility (26.57 + 2.49%). The findings provide an important background in understanding the pollen quality and intraspecific interaction among indigenous rice bean (V. umbellata) accessions in Barili, Cebu to improve production and hybridization.