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Grain filling in wheat crops grown in semiarid regions may depend more on stored water-soluble carbohydrates (WSC) than on current photosynthesis. We evaluated the hypothesis that internode WSC content, specific content (WSC content/internode length), and concentration (WSC content/internode weight) of genotypes affect accumulation and mobilization of stem WSC. Genotypic variation for internode WSC-related traits was measured on the main stem at 10-d intervals in 11 diverse wheats grown under well-watered and droughted field conditions across 2 yr. Relationships among internode WSC-related traits were determined. Date of harvest was the most important factor affecting internode WSC-related traits followed by genotype, irrigation, and year. Genotype x date of harvest was the most important interaction. Drought reduced WSC content, specific content, and concentration in different internodes, except WSC concentration in peduncles. Mobilized WSC from peduncle, penultimate, and lower internodes ranged from 70 to 244 mg, from 95 to 227 mg, and from 175 to 450 mg, respectively. The lower internodes provided 51% of the stem mobilized WSC. Mobilized WSC was higher in well-watered than in droughted conditions for penultimate (164 vs. 135 mg) and lower internodes (274 vs. 244 mg). Drought improved mobilization efficiency in the peduncle, penultimate, and lower internodes by 33, 17, and 11%, respectively. Postanthesis maximum WSC content was highly correlated (r = 0.89 to 0.99) with the amount of WSC mobilized in different internodes, and could be used as a selection criterion to stabilize grain yield under stressful environments.

Wheat crops grown in dryland areas may depend more on stem reserves for grain filling than on current photosynthesis. We evaluated the hypothesis that internode length, weight, and specific weight of genotypes affect accumulation and mobilization of stem reserves. This knowledge might complement selection in stressful environments. Genotypic variation for internode characteristics and their effects on dry matter accumulation and mobilization were measured at 10-d intervals in 11 diverse wheat cultivars grown under well-watered and droughted field conditions across 2 yr. Relationships among internode characteristics and accumulation and mobilization of stem reserves were determined. The main effect of year, irrigation, genotype, and harvest date and genotype x harvest date interaction were significant. Internode length, weight, and specific weight were reduced under drought. Mobilized dry matter from peduncle, penultimate, and the lower internodes ranged from 43 to 171, 81 to 272, and from 198 to 474 rag, respectively. Mobilized dry matter was less in well-watered than in droughted conditions for peduncle (93 vs. 110 mg) but not for penultimate (173 vs. 143 mg) and the lower internodes (331 vs. 304 rag). Drought increased mobilization efficiency, expressed as percentage of maximum dry mater mobilized, in the peduncle, penultimate, and the lower internodes by 65, 11, and 5%, respectively. Stem maximum specific weight was correlated (r = 0.64) with stem mobilized dry matter. Balanced partitioning of stem length into upper and lower internodes and internode maximum specific weight are important in genotypic accumulation and mobilization of stem reserves in wheat., IN SEMIARID AREAS of the world with a Mediterranean climate, rainfall decreases and soil evaporation increases in spring when bread wheat (Triticum aestivum L.) enters the grain-filling period. Wheat crops [...]

The impact of urea nitrogen fertilization on silverleaf whitefly, Bemisia argentifolii Bellows & Perring, population dynamics was examined in field-grown cotton (Gossypium hirsutum L.). Five urea nitrogen treatments were tested, consisting of soil applications of 0, 112, 168, and 224 kg nitrogen per hectare, and a combined soil-foliar application of 112:17 kg nitrogen per hectare. A positive response was observed between N application rates and the measured levels of nitrate N in petioles from mature cotton leaves. Similarly, a positive response was observed between N application rates and the numbers of adult and immature whiteflies appearing during population peaks. To determine whether these positive responses were related, we measured the levels of dietary N compounds (proteins and free amino acids) that would be available for insect nutrition in cotton petioles at the different N application rates. Sampling dates and N application treatments affected levels of soluble proteins in cotton petioles, and interactions between sampling dates and treatments were significant. Across all sampling dates, the relationship between N application rates and levels of soluble proteins was linear. Sampling dates also affected levels of total and individual free amino acids. Fertilizer treatments only affected levels of total amino acids, aspartate, asparagine, and arginine plus threonine. Levels of aspartate or asparagine and the N application rates were linearly correlated. No significant correlations were observed between levels of dietary N compounds in cotton petioles and numbers of whiteflies, either adults or immatures, on the cotton plants. [ABSTRACT FROM AUTHOR]