Variation in pollen viability among Leptochloa crinita accessions: implications for directed crosses

Abstract

Leptochloa crinita, a native forage grass from American arid regions, is widely used for range grazing and revegetation of degraded lands. Despite its importance, progress in breeding and genetic research has been hindered by the difficulty of achieving sexual crosses between L. crinita plants. We hypothesize that factors associated with pollen quality can influence the effectiveness of directed sexual crosses in this species. Thus, the present study investigated pollen viability and longevity in a genetically diverse collection of 21 L. crinita accessions. Pollen viability was estimated at 0, 30, 60, and 180 minutes after anthers dehiscence (MAAD) by two methods: 1) acetocarmine staining; and 2) in vitro germination of pollen grains in culture media containing 0.4-1.0 M sucrose. The staining method overestimated pollen viability, whereas the in vitro germination assay provided accurate and reliable estimates, being 0.6 M the optimal sucrose concentration in the medium, in terms of germination rates and discriminatory power among the accessions. In all the accessions, pollen viability was highest at 0-30 MAAD, and decayed very rapidly, to reach levels below 5% at 180 MAAD. Significant (p<0.05) and broad variation for pollen viability was found among the accessions, with mean values in the range of 49-89% (0 MAAD), 32-76% (30 MAAD), 24-45% (60 MAAD), and 0.6-4.9% (180 MAAD), allowing the identification of six accessions exhibiting the greatest pollen viabilities. These results suggest 0-30 MAAD and using the selected (best) pollen donors, on emasculated female parentals, as the optimal conditions for attempting sexual crosses in L. crinita.