DIALLEL ANALYSIS OF IN SITU DEGRADABILITY OF CORN SILAGE DRY MATTER

Abstract

One of the best ways of evaluating the quality of the silage of a corn cultivar is through the degradability of the whole plant. The existence of genetic variability for this trait has been shown in a number of studies. However, there is little information on its genetic control and breeding alternatives which may be utilized. Considering the importance of digestibility in obtaining a high quality corn silage, this work aims at obtaining information on its genetic control in order to help future breeding programs. For this purpose, 12 lines previously selected were used, 6 being of greater and 6 of lower degradability, to make up a 6 x 6 partial diallel, plus the parental lines. The seeds of the hybrids and of the respective lines were sown in an experimental area of the UFLA at two sowing seasons (November and December). For each season an experiment was set up in 6 x 6 triple lattice for the hybrids and a RBD experiment with three replications for the lines. At the hard-dough stage, the plants were harvested, ground, homogenized, oven-dried at 55oC until constant weight, and then ground again to be tested. For evaluation of the degradability of the silages, in situ dry matter degradability (ISDMD) was employed and four fistulated cows were given the samples of the plots which were incubated for 24 hours. The analysis of the diallel was proceeded by utilizing Gardner and Eberhart’ methodology 1966) and was adapted to the partial diallel by Miranda Filho and Geraldi (1984). It was found that the delay at sowing time reduced corn silage degradability; hence its quality. Manifested heterosis was of low magnitude, contributing on average with less than 7% to the performance of the crosses evaluated. The predominance of additive effects to the inheritance of the trait was verified. It became clear that the best breeding strategy to produce corn cultivars for silage production is by crossing parents with high ISDMD and good combining abilities for characters, being heterosis highly important