Based on principal component analysis, it is concluded that higher pollen germination percentages and longer pollen tubes under optimum conditions and with optimum temperatures above 32 degrees C for pollen germination would indicate tolerance to high temperature.

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Plant reproduction is highly vulnerable to global climate change components such as carbon dioxide concentration ([CO(2)]), temperature (T), and ultraviolet-B (UV-B) radiation. The objectives of this study were to determine the effects of season-long exposure to treatments of [CO(2)] at 360 (control) and 720 micromol mol(-1) (+CO(2)), temperature at 30/22 degrees C (control) and 38/30 degrees C (+T) and UV-B radiation 0 (control) and 10 kJ m(-2) d(-1) (+UV-B) on flower and pollen morphology, pollen production, germination, and tube lengths of six soybean genotypes (D 88-5320, D 90-9216, Stalwart III, PI 471938, DG 5630RR, and DP 4933RR) in sunlit, controlled environment chambers. The control treatment had 360 micromol mol(-1) [CO(2)] at 30/22 degrees C and 0 kJ UV-B. Plants grown either at +UV-B or +T, alone or in combination, produced smaller flowers with shorter standard petal and staminal column lengths. Flowers so produced had less pollen with poor pollen germination and shorter tube lengths. Pollen produced by the flowers of these plants appeared shrivelled without apertures and with disturbed exine ornamentation even at +CO(2) conditions. The damaging effects of +T and +UV-B were not ameliorated by +CO(2) conditions. Based on the total stress response index (TSRI), pooled individual component responses over all the treatments, the genotypes were classified as tolerant (DG 5630RR, D 88-5320: TSRI >-790), intermediate (D 90-9216, PI 471938: TSRI <-790 to >-1026), and sensitive (Stalwart III, DP 4933RR: TSRI <-1026). The differences in sensitivity identified among genotypes imply the options for selecting genotypes with tolerance to environmental stresses projected to occur in the future climates.

No abstract

Temperature is a major environmental factor that affects cotton (Gossypium hirsutum L.) production. Temperatures of 35 to 40°C are frequently observed in cotton‐producing areas. High‐temperature environments are sometimes associated with cotton sterility and boll retention problems; however, there is little specific information available on cotton sensitivity to temperature. We conducted a series of experiments in naturally lit growth chambers where the temperature was accurately controlled so we could measure its effects on cotton fruiting site production, abscission of flower buds (squares), flowers, and bolls. Cotton plants grown from seedlings at 40°C for 12 h d−1 shed all their squares. Plants grown from seedlings in the natural environment, then exposed to daytime temperatures of 30, 35, or 40°C during the fruiting period accumulated 47, 5.7, and <1%, respectively, of their mass as bolls. The time of day when plants were exposed to high temperature did not influence percent boll retention. Number of bolls produced, bolls retained, and percent retention were progressively reduced as time per day at 40°C was increased. Three week exposure to 40°C for 2 or 12 h d−1 resulted in 64 or 0% bolls, respectively, retained on the plants. Cultivars appeared to be similar in sensitivity to high temperature. Cultivars tolerant to short periods of high temperature would probably be more productive in today's environment and increased tolerance to high temperature will be even more essential in a warmer environment.