Seedlings of upland cotton ( Gossypium hirsutum L.) are vulnerable to the partial or complete loss of their cotyledons due to an array of biotic and abiotic causes. These experiments were conducted in the field over a 4‐yr period to determine the effects of such losses in the early vegetative cotyledon growth stage on lint yield, selected lint yield components, and fiber traits. Loss of half a cotyledon apparently stimulated the cotton plant to over compensate for lint yield by 4 to 6%. Overcompensation was not detected for the lint yield components or fiber traits. The plant compensated for the loss of up to one cotyledon in all traits except fiber strength in one year. Loss of one and one‐half cotyledons reduced lint yield (11–33%), picked lint percentage (up to 2.1%), pulled lint percentage (0.4%), micronaire (up to 0.2 units), and fiber elongation (up to 0.3%). Loss of both cotyledons reduced lint yield (81–100%), picked lint percentage (up to 4.6%), pulled lint percentage (4.7%), boll size (0.85 g boll −1 ), micronaire (up to 1.6 units), and fiber elongation (up to 1.4%). Fiber length and length uniformity were not affected at any level of cotyledon removal. Fiber strength exhibited significant differences among treatments in one experiment, but no trend. The elimination of both cotyledons when the first true leaf was about the size of a dime was considerably less harmful to the plant than when done earlier in the season.
Transgenic cotton (Gossypium hirsutum L.) with the Bollgard (BG) genes, the Roundup Ready (RR) gene, or both (BG/RR) has been grown commercially since 1996, 1997, and 1997, respectively. Because genes used in the past for one purpose have often had unforeseen effects on nontargeted traits, these experiments were conducted with cotton across several genetic backgrounds to determine whether the BG, RR, and BG/RR genes have an effect on lint yield, two measures of lint percentage, and five fiber quality traits. Replicated field trials were conducted as if for conventional (i.e., nontransgenic) cotton at two irrigated locations in Oklahoma over 2 years. The BG genes were stable for lint yield across genetic backgrounds, but the RR gene was not. BG significantly increased lint yield across genetic backgrounds in three of four experiments (from 6.7 to 11.8%) with an average of 6.2% over all four. In one background, RR decreased lint yield in two experiments (from -7.3 to -22.2%), but increased it (12.7%) in another. RR increased yield (10.5%) in another background in one experiment, but had no influence in two other backgrounds. Clearly, RR can reduce lint yield in some backgrounds in some environments. BG/RR increased lint yield by 2.5 and 16.8% in two backgrounds over four experiments. In BG/RR, higher yields associated with BG apparently overcame the occasional deficits associated with RR by 7.2 to 9.6%. BG/RR increased lint yield by 8.6 and 9.0% above RR in two backgrounds over four experiments. In another background, the increase was not significant. BG/RR (like BG) often increased lint yield in individual experiments, but caused no significant yield reductions. BG reduced picked lint percentage (-0.7%) and fiber fineness (-0.1 to -0.2 micronaire units). RR increased pulled lint percentage (0.8%), had a neutral or negative effect (-0.3 to -1.0 mm) on fiber length, and showed a neutral or positive effect (0.2 to 0.4 units) on fineness. BG/RR reduced fiber length (-0.3 to -0.8 mm), length uniformity (0.7 to -1.1%), strength (-8.9 kN m kg -1 ), and elongation (-0.2 to -0.4%), but it increased fineness (0.1 units). Relative to RR, BG/RR had a neutral or negative influence on picked lint percentage (as much as -1.2%), fiber length uniformity (-0.1 to 0.7%), fineness (-0.4 units), and strength (-10.3 kN m kg -1 ). Traits not mentioned above were mixed in the direction of their response or were too small to be of statistical significance or practical value.
The importance of fungicide seed treatments on cotton was examined using a series of standardized fungicide trials from 1993 to 2004. Fungicide seed treatments increased stands over those from seed not treated with fungicides in 119 of 211 trials. Metalaxyl increased stands compared to nontreated seed in 40 of 119 trials having significant fungicide responses, demonstrating the importance of Pythium spp. on stand establishment. Similarly, PCNB seed treatment increased stands compared to nontreated seed for 44 of 119 trials with a significant response, indicating the importance of Rhizoctonia solani in stand losses. Benefits from the use of newer seed treatment chemistries, azoxystrobin and triazoles, were demonstrated by comparison with a historic standard seed treatment, carboxin + PCNB + metalaxyl. Little to no stand improvement was found when minimal soil temperatures averaged 25°C the first 3 days after planting. Stand losses due to seedling pathogens increased dramatically as minimal soil temperatures decreased to 12°C and rainfall increased. The importance of Pythium increased dramatically as minimal soil temperature decreased and rainfall increased, while the importance of R. solani was not affected greatly by planting environment. These multi-year data support the widespread use of seed treatment fungicides for the control of the seedling disease complex on cotton.
