The effects of foliar applications of the photosystem II (PSII) inhibitor metamitron on chlorophyll fluorescence and fruit set were compared in peach and apple trees. Metamitron increased dark-adapted chlorophyll fluorescence, measured as a reduction in Fv/Fm values, in both peaches and apples. Maximum suppression of the normalized ratio of variable fluorescence to maximum fluorescence (Fv/Fm) in peaches occurred 1 to 2 days after application and Fv/Fm values recovered by 7 days after treatment. The effects of metamitron on chlorophyll fluorescence were more persistent in apples compared with peaches. Fv/Fm values in apple declined within 2 days of treatment and did not start recovering until 5 days after treatment or longer. Concentrations of metamitron greater than 200 mg·L−1 were phytotoxic to peach leaves, reducing the leaf chlorophyll concentration as determined by SPAD measurements. At 300 mg·L−1, metamitron reduced fruit set in apple but not in peach. Inclusion of a non-ionic surfactant (Silwett L-77) with metamitron greatly increased its negative effect on Fv/Fm, quantum photosynthetic yield of PSII (ΦPSII), and relative electron transport rate (ETR). These results suggest that metamitron may be a useful thinner in apple but not in peach. Additional information is needed to understand how combining metamitron with existing thinning chemicals might enhance their activity. In particular, caution may be necessary if metamitron is applied as a tank mixture with commercial thinning products that have been formulated with a wetting agent.
Various workers have attempted to develop a root piece planting system for sweetpotato, similar to the system used commercially for potato, but attempts to select and breed sweetpotato clones adapted to root piece planting have met with mixed success. It has been hypothesized this is the result of significant genotype × environment effects, which are complicating phenotype screening. The aim of this work was to investigate genotype × environment interactions and yield stability of sweetpotato grown from cut root pieces. Ten sweetpotato clones were grown from cut root pieces in three locations over three seasons at sites in North Carolina and Mississippi. The study found sweetpotato clones grown from root pieces were influenced by both genetic and environmental factors and that the interaction was often complicated and dependent on the trait being measured. A significant genotype × environment interaction and yield instability were found to be present. Further work will be required to understand the nature of the genotype × environment effects; however, the results suggest programs aiming to develop sweetpotato clones adapted to root piece planting will need to use appropriate multienvironment screening so as to account for genotype × environment effects.
Bermudagrass, Cynodon spp. is one of the most commonly grown turfgrass genera in the southern United States having excellent drought tolerance, but poor tolerance to shade. Developing cultivars tolerant to shade would allow bermudagrass to become more prevalent in home lawns or other recreational areas in the southeast, where trees dominate the landscape. In this field study, nine accessions collected from Pretoria, South Africa were evaluated for their ability to grow under shade with varying fertility treatments. These accessions and cultivars ‘Celebration’, ‘TifGrand’, and ‘Tifway’ were evaluated under 0%, 63%, and 80% continuous shade during 2011–12. For both years, significant differences among shade levels, genotypes, and the interaction of the two were observed. As expected, the progression from 0% to 63% to 80% shade reduced normalized difference vegetation index (NDVI), percent turfgrass cover (TC), and turf quality (TQ) readings for all accessions. Some genotypes, however, were able to maintain adequate quality and aggressiveness under 63% shade. ‘Celebration’, WIN10F, and STIL03 performed better than ‘Tifway’ (P ≤ 0.05), the susceptible control. Overall, our results indicate that there are promising genotypes among the bermudagrass materials collected from South Africa. These accessions represent additional sources of shade hardiness to be used in bermudagrass breeding. Furthermore, higher nitrogen fertility provided increased NDVI and TQ in some instances suggesting an added benefit of fertility under low-light conditions. However, the increased economic value attributed to the added inputs associated with these increases is outweighed by the low impacts offered.