Cell Death Patterns in Stalks of a “Supersweet” Sweet Corn Cultivar

Abstract

Stalk No. Cell death ratingz Planting Developmental length expanded No. internodes Location date stage DAPy (cm) internodes 1 2–4 5–11 Overall Wilburton 18 May Late whorl 48 97 cx 4.7 b 0.0 c 0.0 b 0.0 c 0.0 c Tassel 59 147 ab 9.9 a 2.5 b 3.6 a 2.2 b 2.6 b Silk 69 140 b 9.6 a 3.6 a 4.0 a 4.0 a 4.0 a Mature silk 76 154 a 9.3 a 3.4 a 4.0 a 4.0 a 3.9 a Harvest 88 156 a 9.3 a 3.6 a 3.9 a 3.9 a 3.9 a Lane 15 June Late whorl 40 172 c 9.8 b 1.6 d 2.5 b 0.2 b 0.9 b Tassel 46 208 b 10.8 a 2.9 b 4.0 a 3.4 a 3.5 a Silk 54 217 a 10.8 a 2.2 c 3.9 a 3.9 a 3.8 a Mature silk 61 213 ab 10.4 a 2.1 c 3.9 a 4.0 a 3.8 a Harvest 68 208 b 10.5 a 3.4 a 4.0 a 4.0 a 3.9 a 17 July Late whorl 42 131 b 7.5 b 0.8 b 1.9 c 0.0 b 0.7 c Tassel 53 136 b 10.5 a 1.3 ab 3.3 b 3.9 a 3.3 b Dead pith tissue in split dent corn stalks (Zea mays L.) is white and fluffy (Pappelis and Williams, 1966), and it is easily colonized by fungal pathogens, especially Fusarium moniliforme Sheldon (Foley, 1962). In sweet corn, F. moniliforme produces metabolites toxic to plant and mammalian systems (Zummo and Scott, 1992). This fungus asymptomatically and systemically colonizes sweet corn tissues, including kernels (Bacon et al., 1992). Infection through nodes can result in colonization of ears if tissue subtending the inflorescence and shank are in advanced stages of senescence. Dent corn cultivars have some resistance to diplodia, gibberella, or fusarium stalk rots before silking, but they differ in susceptibility later (Koehler, 1960). Sweet corn cultivars are different from dent corn because they contain endosperm mutant genes controlling kernel sweetness (Courter et al., 1988). Planting later delays cell death in dent corn stalk internodes (Pappelis and Boone, 1966). Whether stalk cell death patterns in ‘Florida Staysweet’ sweet corn , an sh2 (shrunken-2) genotype, are similar to those in dent corn is unknown. Neither senescence rates nor causes that contribute to senescence in supersweet corn are well known. Our experiment was designed to determine if planting date affected senescence in stalk tissues in ‘Florida Staysweet’. On 18 May 1990 in Wilburton, Okla., and on 15 June and 17 July 1990 in Lane, Okla., seeds were sown with 0.23-m in-row spacing in single rows on beds with 0.9-m centers. Plantings were replicated four times. Fields were fertilized with ammonium nitrate (34N– 0P–0K), P2O5 (0N–46P–0K), and K2O (0N– 0P–60K) to bring nutrient levels to (in kg•ha) 100N–134P–134K. The principal water source was precipitation, but additional water was supplied weekly from tassel emergence through kernel filling by drip irrigation equivalent to 50 mm of precipitation per application. Beginning at the late whorl stage (collar of twelfth leaf present, ≈43 days after planting) and con-