Seleção recorrente intrapopulacional em progênies de meios-irmãos de milho em condições contrastantes de nitrogênio

Abstract

The development of open-pollinated varieties (VPA’'s) in low use of nitrogen (N) conditions is of great value, especially for the production systems of small farmers, predominant in the region Center-South, that have limited capital and cannot to invest in production technologies. The objectives of this study were to initiate a intrapopulation selection recurrent cycle of half-sib progenies (PMI), in two locations, Dourados e Caarapó, MS, as part of a cyclical process of developing a VPA's in low use of nitrogen conditions, as well as, estimate genetic parameters and compare two selection indexes, proposed by Smith (1936) and Hazel (1943) and Mulamba and Mock (1978). It also evaluate the genotypic divergence of the PMI selected the two locations studied. In the second crop 2015 was conducted the test evaluation consists of the 220 PMI selected in each environment. The PMI were allocated in two contrasting environments of nitrogen, high N (120 kg ha-1) e low N (0 kg ha-1), in both locations, under incomplete blocks in lattice 15x15 design with 3 replications for each environment. The analysis of variance showed different behavior of the progenies in the face of environmental fluctuations and the PMI showed enough variability to advance the intrapopulation recurrent selection program. Heritability estimates based on the average of progenies for high N characteristics changed from 62,89 to 95,81% and the 𝑏 ̂ index changed from 1,30 to 3,09. In low N heritability coefficient changed from 23,90 to 82,81%. For 𝑏 ̂ index variation was from 0,56 to 2,20. The estimated heritability coefficient and index b for grain yield were higher at high N, being able to obtain greater genetic gain in this population. The Mulamba and Mock index achieved the greatest gains predicted by selection for most of the characteristics in the two studied locals and two nitrogen contrasts. The index Smith and Hazel achieved the highest predicted gains for the characteristic grain yield in both studied locals and two nitrogen contrasts. There was a higher genetic divergence for high and low N in Dourados.