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.

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.

Cotton (Gossypium hirsutum L.) crop, cultivated between 40 degrees N and 40 degrees S, is currently experiencing 2-11 kJ m-2 d-1 of UV-B radiation. This is predicted to increase in the near future. An experiment was conducted to study the effect of enhanced UV-B radiation on vegetative and reproductive morphology and leaf anatomy of cotton in sunlit, controlled environment chambers. From emergence to harvest, cotton plants were exposed to 0, 8 or 16 kJ m-2 d-1 of UV-B in a square wave approach for 8 h from 0800 to 1600 h. Changes in plant height, internode and branch length, mainstem node number, leaf area, length and area of petals and bracts, and anther number per flower were recorded. Epidermal cell and stomatal density, stomatal index, leaf thickness, and epidermal, palisade and mesophyll tissue thickness were also measured. Initial chlorotic symptoms on leaves turned into necrotic patches on continued exposure to enhanced UV-B. Exposure to high UV-B reduced both vegetative and reproductive parameters and resulted in a smaller canopy indicating sensitivity of cotton to UV-B radiation. Enhanced UV-B radiation increased epicuticular wax content on adaxial leaf surfaces, and stomatal index on both adaxial and abaxial leaf surfaces. Leaf thickness was reduced following exposure to UV-B owing to a decrease in thickness of both the palisade and mesophyll tissue, while the epidermal thickness remained unchanged. The vegetative parameters studied were affected only by high levels of UV-B (16 kJ m-2 d-1), whereas the reproductive parameters were reduced at both ambient (8 kJ m-2 d-1) and high UV-B levels. The study shows that cotton plants are sensitive to UV-B at both the whole plant and anatomical level.

Diagnostic methods assaying leaf optical properties can aid rapid site‐specific screening of crop nitrogen status. A set of calibration curves relating many 1.5‐nm band reflectance ratios to cotton (Gossypium hirsutum L.) leaf N concentration was established from plants grown in sunlit growth chambers and at a range of nitrogen levels. Predicted and actual concentrations were compared by regression for a validation set of field‐grown leaf samples from diverse genotypes. Only those ratios that combined a red‐edge measure (700 or 716 nm) with a waveband of high reflectance in the very near infrared region (755–920 and 1000 nm) provided good precision (correlation) and accuracy (one‐to‐one relationship between predicted to actual values). Other indices that included a chlorophyll‐based reflectance feature also had good precision but were less accurate than those obtained from the red‐edge/very‐near‐infrared reflectance ratios.

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.