Genetics of Parenchyma Cell Death in Corn Stalk Internodes and Leaf Midribs

Pith (parenchyma) cell death (PCD) in stalk internodes of corn (Zea mays L.) is positively associated with stalk rot. Only limited information on inheritance of PCD is available, and none for corn with the leafy (Lfy) gene. The objectives of this study were to (i) estimate general (GCA) and specific combining ability (SCA) effects, (ii) determine the effect of the Lfy gene on PCD and leaf midrib parenchyma cell death (LMCD) among 21 F₁ crosses from seven Lfy synthetics (A619, A632, B73, Hy, Mo17, wf9, and 914), and (iii) determine if LMCD is correlated with PCD. In 1989 and 1990, we visually rated LMCD of five Lfy and five non-Lfy plants (5 leaves plant⁻¹) ≈1 wk before midsilk. Then for PCD, 21 d after midsilk, we visually rated the first four stalk internodes above the brace roots of all plants (1988) or 10 Lfy and 10 non-Lfy plants in each plot (1989 and 1990). For PCD, SCA was more important than GCA, as suggested by small ratios (0.32 and 0.18) of GCA (σ²ₛ) and SCA (σ²g) variances computed using 2σ²g/(σ²g + σ²g). The A632, B73, and Mo17 synthetics showed significant negative GCA effects for PCD; their use in a breeding program might be effective in reducing stalk internodal parenchyma cell death. Use of F₁ crosses Mo17 syn × 914 syn, A619 syn × Mo17 syn, and B73 syn × Hy syn should be avoided, as they showed significant positive SCA effects for PCD. Evaluation of all four stalk internodes might not be necessary, as the third internodes provided more reliable PCD data than the others. Pith cell death was significantly lower in the Lfy than the non-Lfy plants. Leaf midrib cell death and PCD were not correlated genetically or phenotypically, which suggests that selection for LMCD would not change PCD. A 2σ²g/(σ²g + σ²ₛ) ratio of 0.59 for LMCD suggests that both GCA and SCA are important. The A632 syn and B73 syn showed significant negative and 914 syn showed significant positive GCA effects for both LMCD and PCD. Mean LMCD (across leaves) of Lfy plants was significantly lower than that of non-Lfy plants in two of three environments. Approved for publication by the Director of the Louisiana Agric. Exp. Stn. as Manuscript no. 91-09-5490. Part of a dissertation submitted by S. Dronavalli in partial fulfillment of the requirements for a Ph.D. degree.