HONOLULU, HAWAII
University of Hawaii

Comparison of husk leaves using visual score rating and direct measuring methods in maize (Zea mays L.)

— Ji, HC; Brewbaker, JL

Husk leaves (or “flag leaves”) extend terminally from the ear husks of maize (Zea mays L., corn). They diverge from ligules at the tip of the husk, simulating the relationship of the leaf blade to leaf sheath. Husk leaves are typical of temperate sweet corns, where they facilitate machine-handling and removal of husks prior to canning. Most field corns lack or have very reduced husk leaves.

The inheritance of husk leaves was studied by generation mean analysis of progenies derived from crosses of the inbreds Hi38c1 and Ia453sh2. The Hi38c1 inbred is a tropical Hawaiian super sweet that lacks husk leaves and is based on the gene brittle-1. The Ia453sh2 inbred is a conversion to shrunken-2 of the Iowa sweet inbred, and has typical long husk leaves. The parents and all progenies were planted in randomized complete block (RCB) designs with three replications in summer of 2003 at Waimanalo Research Station, University of Hawaii on Oahu.

We wanted to compare results by two methods to find if one has an advantage over the other. One of the methods used is the direct measuring method [method I] using a ruler, and the other is the visual score rating method [method II] following husk leaf extension. The objective of this study was to obtain more useful methods to investigate the genetics of husk leaves between visual score rating and direct measuring methods in sweet corn inbreds Ia453 sh2 (with husk leaves) and Hi38c1 (without) by means of generation mean analysis (GMA).

Using method I, average husk leaves length was 1.86cm (Hi38c1) and 13.20cm (Ia453sh2). The F1 hybrids averaged 11.06cm, while the F2 averaged 12.10cm. Backcross families averaged 6.04cm and 14.74cm, respectively. Coefficient of variation (CV) averaged as follows; P1 53%, P2 33%, F1 47%, F2 75%, BC1 93%, BC2 50%.

Husk leaf extension was scored in the summer season on a scale of 1 (no husk leaves) to 9 (very long extension). The parents’ average scores were 1.25 (Hi38c1) and 6.07 (Ia453sh2). The F1 hybrids averaged 4.14, while the F2 averaged 3.55. Backcross families averaged 2.43 and 4.44, respectively. Coefficients of variation (CV) averaged as follows: P1 35%, P2 32%, F1 40%, F2 66%, BC1 61%, BC2 56%.

The two results were analyzed following the Generation Mean Analysis (GMA) Method modified from Gamble (1962) and Mather & Jinks (1977). Generation mean analysis of the six generations (Table 1) revealed no significant dominance effect but showed an additive effect. Because the aa [additive × additive] and dd [dominance × dominance] effects had opposite signs, a duplicate dominant or recessive suppressor type of epistasis was indicated (Mather and Jinks, 1982).

According to methods I and II, the broad-sense heritability averaged 77.55% and 56.23%, respectively, and the narrow-sense heritability averaged 65.64% and 44.28%, respectively. An estimate of minimum number of effective gene loci, based on Castle and Wright formulas, was 0.29 and 1.10 in methods I and II.

Therefore, both methods showed that husk leaves depend on a single gene acting without a dominance effect, and we consider that it is advantageous to adopt the visual score rating method rather than the direct measuring method due to the time and labor involved with the latter.

Table 1. Estimates of additive, dominance, and interaction parameters for the cross Hi38c1 (bt) × Ia453 sh2.

† m=midpoint, a=additive genetic effect, d=dominance effect, aa=additive × additive effect, ad=additive × dominance effect, dd=dominance × dominance effect
*, **, NS: levels of significance

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