Estimation of Heat Tolerance Improvement in Recent American Pima Cotton Cultivars

Abstract

Improving cotton (Gossypium spp.) heat tolerance (ability to set bolls in high temperature environments) has been an important aspect of the American Pima (Pima) cotton (G. barbadense L.) breeding program for over 25 years. However, heat tolerance is difficult to quantify. This report estimates change in heat tolerance of Pima cotton through yield response over 30 years in six Arizona counties that differ in elevation and mean summer temperatures. Pima cotton/upland cotton (G. hirsutum L.) lint yield percentages were compared for each county by regression with year of production. County mean yield percentages were also compared with elevations. Pima cotton yields as percentages of upland cotton yields increased in five of the six counties over the 30‐year period. Pima lint yield increased from 57 % of upland yield in 1956 to 75 % in 1985 when averaged over the six counties. This increase represents an estimated 206 kg lint ha‐1 in addition to any upland yield increase. Comparison of regression coefficients suggest that nearly 50 % of the 30‐year lint yield increase of Pima cotton at lower elevations was the result of increased tolerance to high temperature in improved cultivars. County 30‐year mean Pima cotton lint yields as percentage of upland cotton yield increased significantly (P < 0.001) from 52.2% to 82.1 % as county elevations increased from 37 m to 1273 m (cooler summer temperatures). These results support reports of greater heat tolerance for upland cotton than Pima cotton, but also show that the difference between species has been reduced substantially by breeding in the last 30 years.

Photosynthesis and Growth of Cotton (Gossypium hirsutumL.) Lines Deficient in Chlorophyll Accumulation

“…In Pima cotton (Gossypium barbadense), stomatal conductance was correlated with increased lint yields (Lu et al 1998) and was likely responsible for improvements in the plant's ability to control leaf temperature (Kittoch et al 1988;Reddy et al 1992;Lu et al 1998). Lu et al (1998) demonstrated that DP90, a line also studied in this report, had a 25-35% higher stomatal conductance, 35-50% higher photosynthetic rate, and a 45% smaller leaf area than Pima.…”

Heat Stress during Flowering in Summer Brassica

“…The actual physiological mechanisms resulting in reduced seed size or number per pod should be determined. Kittock et al (1988) found that nearly half of the 30% yield improvement in lint yield of new Pima cotton cultivars was the result of increased tolerance to high temperatures, indicating that heat stress is a trait that can be selected for in a plant breeding program. With global warming, heat stress may become more of a problem in the major Brassica growing regions of Canada and to safeguard future yield, plant breeders should be selecting for increased heat stress tolerance.…”

“…H igh air temperatures during reproduction cause a reduction in fertility and seed yield in wheat ( Triticum aestivum L., Saini et al, 1983), corn ( Zea mays L.; Schoper et al, 1987; Mitchell and Petolino, 1988), cotton ( Gossypium spp. ; Kittock et al, 1988), cowpea [ Vigna unguiculata (L.) Walp. ; Ahmed and Hall, 1993], and pea ( Pisum sativum L.; Guilioni et al, 1997).…”

A Comparison of Scenarios for the Effect of Global Climate Change on Cotton Growth and Yield

“…Low-temperature tolerance in cotton would allow producers to plant the crop earlier and permit a crop canopy to be developed earlier in the growing season, allowing flowering to occur before the midsummer high temperatures that limit fruit set. Several studies have attempted to determine the negative impact of high temperatures on cotton yields in Arizona (Kittock et al 1988;, where cotton yields are also limited by high temperatures. Their findings indicate that cotton cultivars tolerant to high temperature transpired more water than high-temperature sensitive cultivars.…”