Response of a Maize Synthetic to Recurrent Selection for Stalk Quality1

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Abstract
Recurrent selection, based on S1 lines in replicated experiments, was used in separate trials for three cycles to improve the maize (Zea mays L.) synthetic BS1 for resistance to artificial stalk rot (Diplodia maydis) and resistance to mechanical stalk breakage. The cycle populations (BS1 and C1 to C3 for BS1SR and BS1MS for stalk‐rot and stalk‐strength selection, respectively), populations crossed to a low‐stalk‐quality single cross, and crosses of populations between each procedure of selection were evaluated for stalk and rind strength, Diplodia stalk rot, field stalk rot, and field stalk and root lodging. Random S1 lines from BS1 and C3 populations of BS1SR and BS1MS were evaluated for Diplodia stalk rot and stalk and rind strength. Highly significant improvements were observed for all stalk‐quality traits. Changes from the CO to BS1MSC3 and BSISRC3, respectively, were as follows: stalk strength, 34.8 to 56.5 and 46.7 kg; Diplodia stalk‐rot rating, 3.5 to 1.8 and 1.7; rind strength, 3.4 to 4.2 and 4.3 kg; field stalk‐rotted plants, 25 to 5 and 8%; and field stalk‐lodged plants, 13 to 6 and 3%. Improvements in population crosses, population testcrosses, and random S1 lines closely paralleled the improvements in the populations per se, indicating that stalk quality is controlled primarily by additive type gene action. Highly significant correlations were observed among all stalk‐quality traits. Recurrent selection for rind strength and stalk‐rot resistance, simultaneously, may be the most desirable method of improving populations for development of inbred lines with superior field stalk quality.