Growth Analysis of Maize Variety Hybrids Obtained From Two Recurrent Selection Programmes for Grain Yield*

SUMMARY A reciprocal recurrent selection programme was initiated in 1949 to improve the grain‐yield performance of Iowa Stiff Stalk Synthetic [BSSS(R)] and Iowa Corn Borer Synthetic no. 1 [BSCB(R)] maize ( Zea mays L.) populations. In the same year, a half‐sib selection programme was initiated in an open‐pollinated maize variety, ‘Alph’ (i.e. BS12), with the same objective. Inbred B14 was the tester variety in the half‐sib programme. Previous studies showed that significant grain‐yield increases resulted from seven cycles of reciprocal recurrent selection and six cycles of half‐sib selection. Growth analysis was used to examine productivity and distribution of dry matter by the unimproved and improved variety hybrids of BSSS(R) × BSCB1 (R)and BS12 × B14A. Only leaf area, leaf‐area duration, leaf‐area index, and leaf‐area index duration were significantly larger in the improved than the unimproved hybrids. These differences occurred mostly during grain filling. Evidently, increased grain yields from recurrent selection in these programmes were consequences of prolonged photosynthetic activity, increased production of photosynthate during grain filling, and increased translocation of photosyntheate from source to sink, in both BSSS(R) × BSCBl(R) and BS12 × B14A.