New streak resistant maize lines derived from the Vaalharts composite

Abstract

Experimental white and yellow maize inbred lines of US Corn Belt derivation were improved for streak resistance using the improved Vaalharts Composite in yellow kernel colour (VHC2) and its counterpart in white (VHCW) as donor parents. Using natural infection and a programme of full-sib family selection, high levels of resistance were obtained after five cycles of recurrent selection. At the S5 level of inbreeding the inbred line I137TN served as tester in crosses with 165 yellow and 125 white resistant lines. In a replicated field trial with a high streak potential, 35 test crosses (18 in yellow and 17 in white) were identified which significantly out-yielded two commercial standards and showed particular agronomic promise. Of these, twelve in each colour group were subsequently crossed to the lines R2565Y (yellow) and R119W (white), both in an 1137TN/K64R background. In a field trial at Vaalharts, grain yield of all 24 experimental crosses compared favourably with those of two commercial standards, at the same time showing pronounced resistance to streak. The 35 lines as well as the 24 hybrid combinations are available for release. All lines have medium length of growing season requirements and are of dent or semi-dent kernel type.