INTROGRESSION OF EXOTIC MAIZE GERMPLASM FOLLOWED BY SELECTION FOR STALK QUALITY AND GRAIN YIELD (MASS SELECTION, DESIRED GAIN INDEX, PENETROMETER MEASUREMENTS).

摘要

Two maize (Zea mays L.) populations, RSSSC (adapted to central Corn Belt) and South African Photoperiod Insensitive Composite II (PIC2: tropical origin), were crossed and the F(,1) was backcrossed once to RSSSC. Random sets of at least 80 - 100 S(,1) families were derived from RSSSC, BC(,1)-F(,2), F(,2), and PIC2 populations (with 0, 25, 50, and 100% exotic germplasm, respectively). These were evaluated in 1983 and 1984 for grain yield, pollen-shed date, penetrometer reading, stalk rot and leaf blight severity, and other agronomic traits. In the F(,2), based on the evaluation in 1983, one cycle of divergent S(,1) selection was completed for the following traits: (1) grain yield, (2) lodging, (3) rind penetrometer readings, (4) stalk crushing strength, and (5) a desired gain selection index based on the first 3 traits. In addition, one cycle of divergent mass selection for penetrometer measurements was completed. Evaluation of progress from selection was based on cycle 1 synthetics, testcrosses to FRMo17 and Oh43, and on random cycle 1 S(,1) families grown in 1984 and/or 1985.;In the F(,2), response to S(,1) selection was significant for all 5 traits. Selection for higher grain yield resulted in a deterioration of stalk quality. Index selection was effective in increasing grain yield while maintaining acceptable lodging resistance. For improving lodging resistance, selection for lodging, per se, was most effective followed by selection for penetrometer measurements and stalk crushing strength. However in testcrosses, the penetrometer selections showed greatest gains in lodging resistance. Mass selection for penetrometer measurements was as effective as S(,1) selection. The penetrometer is a reliable tool for assessing stalk quality of maize.;Mean grain yields for RSSSC, BC(,1)-F(,2), F(,2), and PIC2 were 3.31, 3.08, 2.88, and 1.96 t/ha, respectively. Highest genetic variance estimates for yield were obtained in BC(,1)-F(,2). Pollen-shed in RSSSC was 10 days earlier than in PIC2. Introgression of PIC2, as expressed in the BC(,1)-F(,2) and F(,2), improved the poor stalk rot and leaf blight resistance, and the low rind puncture strength of RSSSC. Predictions of gain from selection for grain yield, per se, indicated that BC(,1)-F(,2) would be the most favorable foundation population. However, a desired gain performance index including grain yield, grain moisture, penetrometer reading, and stalk rot and leaf blight ratings favored the F(,2) if little weight was given to yield and declared RSSSC, BC(,1)-F(,2), and F(,2) as equally valuable foundation populations if considerable weight was assigned to yield. PIC2 was disqualified mainly due to its lack of adaptiveness.