The structures of two derivatives of 2‐hydroxy‐1,4‐naphthoquinone (lawsone) are examined using the density functional theory (DFT) hybrid functional B3LYP. Using the optimized structure of lawsone acetate, the reactivity of acyl transfer is described. Also, the nucleophilicity of the conjugate base of lawsone is predicted using the conceptual descriptors related to softness within the DFT framework. Copyright © 2008 John Wiley & Sons, Ltd.

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Two experiments were conducted to evaluate the effect of banana (Musa AAA) leaf pruning intensities at flower emergence on fruit yield and black Sigatoka leaf infection. In both experiments a decreasing linear effect of leaf pruning intensities was observed on the number of functional and total leaves of the parental plant at harvest. Leaf pruning intensities did not affect bunch weight and fruit length in any experiment. As leaf pruning intensity increased there was a significant rectilinear increase in the flowering index in the first, second and third flowering ratoon crops. In the plant crop experiment black Sigatoka variables were not affected by leaf pruning. However, in the ratoon crops experiment, as leaf removal increased, black Sigatoka severity decreased at 4 and 8 weeks, and was similar at 11 weeks after flower emergence. The results support leaf pruning at flower emergence as a tool for inclusion in the integrated management of black Sigatoka severity, because there was either no reduction in bunch weight or any change in ratooning times.

The reproduction and pathogenicity of Helicotylenchus multicinctus, Meloidogyne incognita and Pratylenchus coffeae was studied on Musa AAA cv. Grande Naine pot plants and microplot plants. First, separate experiments using different inoculation numbers (between 218 and 4144) and different exposure times (between 8 and 22 weeks) were executed in pots for each nematode species. Helicotylenchus multicinctus suppressed root growth by 13%, comparing inoculated with uninoculated plants. In contrast, M. incognita stimulated root growth by 6.7%, while P. coffeae had no effect on root growth. The interaction between R. similis and each of these three nematode species was investigated in a concomitancy experiment in pots. Plants without concomitant species yielded the highest R. similis population densities but did not differ from plants previously inoculated with H. multicinctus and P. coffeae. Meloidogyne incognita was the only concomitant species that reduced R. similis population densities. Inoculation with R. similis affected the recovered numbers of P. coffeae albeit with large variability. In the microplot experiment, all four nematode species except H. multicinctus reduced the bunch weight of bananas, compared to uninoculated plants. Pratylenchus coffeae and R. similis increased root damage by 129 and 262%, respectively, while only the latter species suppressed root weight with 66%.

An analysis of the plant-parasitic nematodes found on the banana (Musa AAA) plantations in the provinces of Cañar, El Oro, Guayas, Los Rios and Santo Domingo of Ecuador from 2008 to 2014 was carried out. The nematode extraction was done from 25 g of fresh roots that were macerated in a blender and from which nematodes were recovered in a 0.025 mm (No 500) mesh sieve. The data were subjected to frequency analysis in PC-SAS and the absolute frequency was calculated for each individual genus. Four plant parasitic nematodes were detected and, based on their frequencies and population densities, the nematode genera in decreasing order was: Radopholus similis > Helicotylenchus spp. > Meloidogyne spp. > Pratylenchus spp. Radopholus similis was the most abundant nematode, accounting for 49 to 66% of the overall root population, followed by Helicotylenchus spp. with 29 to 45% of the population through- out the different analyzed years. From a total of 13,773 root samples, 96% contained R. similis, 91% Helicotylenchus spp., 35% Meloidogyne spp., and 25% Pratylenchus spp. and, when all of the nematodes that were present were pooled (total nematodes), 99.9% of the samples had nematodes. A large number of samples with a nematode population above the economic threshold suggested by Agrocalidad, INIAP and Anemagro (2,500-3,000 nematodes/100 g of roots) was observed in all of the years, the months and the five sampled provinces. The statistical differences (P<0.0001) detected for the nematode frequencies among the years, months and provinces, more than likely, were associated with the high number of samples included in each year, month and province because the variations in the frequencies for each nematode genus were small.