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In the last 8 yr, cotton (Gossypium hirsutum L.) growers in North Carolina have experienced variations in the year-to-year lint yield averages that range from a 56% increase to a 49% decrease. This variability results in wild fluctuations in income and a desire for more stable yields. Genetic structure may contribute to stability. This study was conducted to determine the impact of heterozygosity and heterogeneity on lint yield stability. Lint yield was observed in 18 environments over 3 yr among four population types that included homozygous lines grown in pure stands, homozygous lines grown in blended stands, hybrids grown in pure stands, and hybrids grown in blended stands. Comparisons were made using trait means, standard deviations, and the coefficients of variation (CVs) calculated over environments. There was no significant difference between lines grown in pure stands and blended lines with respect to yield or stability. Hybrids had a lower CV (were more stable) than homozygous lines. This stability was attributed to the hybrids and blends of hybrids out-yielding the homozygous lines and blends of homozygous lines in the low-yielding environments, but having similar yields in the high-yielding environments. These results do not support growing blends to increase stability or yield; however, growing hybrid cultivars could result in increased yields while reducing variability compared with current production practices. [ABSTRACT FROM AUTHOR]

Turfgrass is a highly managed ecosystem subject to frequent fertilization, mowing, irrigation, and application of pesticides. Turf management practices may create a perturbed environment for ammonia oxidizers, a key microbial group responsible for nitrification. To elucidate the long-term effects of turf management on these bacteria, we assessed the composition of betaproteobacterial ammonia oxidizers in a chronosequence of turfgrass systems (i.e., 1, 6, 23, and 95 years old) and the adjacent native pines by using both 16S rRNA and amoA gene fragments specific to ammonia oxidizers. Based on the Shannon-Wiener diversity index of denaturing gradient gel electrophoresis patterns and the rarefaction curves of amoA clones, turf management did not change the relative diversity and richness of ammonia oxidizers in turf soils as compared to native pine soils. Ammonia oxidizers in turfgrass systems comprised a suite of phylogenetic clusters common to other terrestrial ecosystems. Nitrosospira clusters 0, 2, 3, and 4; Nitrosospira sp. Nsp65-like sequences; and Nitrosomonas clusters 6 and 7 were detected in the turfgrass chronosequence with Nitrosospira clusters 3 and 4 being dominant. However, both turf age and land change (pine to turf) effected minor changes in ammonia oxidizer composition. Nitrosospira cluster 0 was observed only in older turfgrass systems (i.e., 23 and 95 years old); fine-scale differences within Nitrosospira cluster 3 were seen between native pines and turf. Further investigations are needed to elucidate the ecological implications of the compositional differences.