Limited Diclosulam Herbicide Uptake and Translocation-Induced Tolerance in Crotalaria juncea.

The study was to identify the potential tolerance of Crotalaria juncea to diclosulam uptake and translocation and its effects on the physiological metabolism of plants. Two experiments were carried out; I-Evaluation of uptake and translocation of 14C-diclosulam (35 g a.i. ha-1) in C. juncea, at seven and 14 days after emergence. II-Evaluation of chlorophyll a transient fluorescence of dark-adapted C. juncea leaves when applied diclosulam in pre-emergence. Plants of C. juncea presented an anatomical/metabolic barrier to diclosulam translocation in the stem, which may confer tolerance to this herbicidal, besides reduced translocation due to low accumulation in the cotyledons. In addition, plants can maintain photosynthetic metabolism active when growing in soil with diclosulam by not changing the dynamics of energy dissipation. Thus, when cultivated in soil with residual of diclosulam, C. juncea can tolerate the herbicide to maintain plant growth.

The geographical and seasonal mosaic in a plant-herbivore interaction: patterns of defences and herbivory by a specialist and a non-specialist.

In order to evaluate the geographic mosaic theory of coevolution, it is crucial to investigate geographical variation on the outcome of ecological interactions and the functional traits which dictate these outcomes. Plant populations are attacked by specialist and non-specialist herbivores and may have different types of chemical and biotic defences. We investigated geographical and seasonal variation in the interaction between the plant Crotalaria pallida and its two major herbivores (the specialist Utetheisa ornatrix and the non-specialist Etiella zinckenella). We first showed that attack by the two herbivores and a chemical and a biotic defence vary greatly in time and space. Second, we performed a common garden experiment that revealed genetic variation among populations in herbivore resistance and a chemical defence, but no genetic variation in a biotic defence. Third, we sampled 20 populations on a much larger geographical scale and showed great variation in attack rates by the two herbivores and a chemical defence. Finally, we showed that herbivory is not correlated with a chemical defence in the 20 field populations. Our study shows that to understand the evolution of ecological interactions it is crucial to investigate how the outcome of the interaction and the important species traits vary geographically and seasonally.

Studying the link between physiological performance of Crotalaria ochroleuca and the distribution of Ca, P, K and S in seeds with X-ray fluorescence.

This study describes the use of X-ray fluorescence spectroscopy in Crotalaria ochroleuca seed technology. This work evaluated X-ray fluorescence techniques to estimate the physiological performance of different C. ochroleuca seed coat colours based on the concentration and distribution of Ca, P, K, and S in seed structures. The treatments consisted of seeds separated by coat colours (yellow, green, and red) and a control treatment (colour mix according to their natural occurrence in commercial lots), and was carried out in a completely randomized design, with four replications. The physiological performance was evaluated by analyzing the water content, germination, first germination count, germination speed index, electrical conductivity, seedling emergence, and seedling length and dry mass. X-ray fluorescence spectroscopy techniques were carried out with quantitative analyses (Ca, P, K, and S concentration in the seed coat and the whole seed) and qualitative analyses (macronutrient mapping). The EDXRF and µ-XRF techniques are efficient and promising to differentiate the physiological performance of C. ochroleuca seeds, based on the concentration and distribution of Ca, P, K, and S in different structures. Ca is predominant in the seed coat, and K, S, and P are found throughout the embryonic axis. Seeds of yellow and green coats have higher nutrients concentration and distribution in the embryonic axis, revealing high germinative capacity and physiological performance. Seeds of red coat have higher nutrients concentration in the seed coat and lower assimilation, showing less vigour, which interferes directly in the quality of commercial lots.

Common-garden experiments reveal geographical variation in the interaction among Crotalaria pallida (Leguminosae: Papilionideae), Utetheisa ornatrix L. (Lepidoptera: Arctiidae), and extrafloral nectary visiting ants.

The study of geographical variation is a key approach to understand evolution of ecological interactions. We investigated geographical variation in the interaction among Crotalaria pallida (Leguminosae: Papilionideae), its specialized herbivore, Utetheisa ornatrix L. (Lepidoptera: Arctiidae), and ants attracted to extrafloral nectaries (EFNs). First, we used common-garden experiments with plants collected in different sites at different geographical scales to test for differences among populations in C. pallida attractiveness to ants. When we compared three populations from Southeast Brazil (150 km apart), the number of visiting ants per plant, and the percent of termite baits attacked by ants, were significantly different among plant populations. In a comparison of populations from SE Brazil and Florida (USA), there was no significant difference between the populations in the number of ants per plant or the frequency of baits attacked. Second, we tested in a common garden if U. ornatrix larvae present any behavior to avoid ant predation, and if there were genetic differences among populations. We observed that most larvae moved away from the vicinity of the EFNs (flowers and fruits) to the plant leaves. Of the larvae that moved to leaves, only 10% were attacked by ants while 89% of larvae that stayed near the fruit/flower were attacked. There was a significant difference among populations in the frequency of larvae that moved to the leaves and the frequency of larvae attacked by ants. We discuss the possible causes of the geographical differences observed and propose future research directions in this system.

The effect of transitional organic production practices on soilborne pests of tomato in a simulated microplot study.

The perceived risk of pest resurgence upon transition from conventional to organic-based farming systems remains a critical obstacle to expanding organic vegetable production, particularly where chemical fumigants have provided soilborne pest and disease control. Microplots were used to study the effects of soil amendments and cropping sequences applied over a 2-year transitional period from conventional to organic tomato (Solanum lycopersicum) cultivation on the incidence of bacterial wilt caused by Ralstonia solanacearum, purple nutsedge (Cyperus rotundus) reproduction, root galling by Meloidogyne incognita, and soil nematode populations. A continuation of tomato monoculture during the transitional period resulted in a disease incidence of 33%, as compared with 9% in microplots that were rotated with sunn hemp (Crotalaria juncea) and Japanese millet (Echinochloa crusgalli var. frumentacea). The benefits of disease control from a crop rotation extended into to a second season of organic tomato cultivation season, where bacterial wilt declined from 40% in microplots with a tomato monoculture to 17% in plots with a crop rotation sequence. Combining applications of urban plant debris with a continued tomato monoculture increased the incidence of bacterial wilt to 60%. During the transition period, tomato plants following a cover crop regime also had significantly lower levels of root galling from root-knot nematode infection compared with plants in the continuous tomato monoculture. Nutsedge tuber production was significantly increased in plots amended with broiler litter but not urban plant debris. Compared with a continuous monoculture, the results illustrate the importance of a systems-based approach to implementing transitional organic practices that is cognizant of their interactive effects on resident soilborne disease, weed, and pest complexes.

Varying herbivore population structure correlates with lack of local adaptation in a geographic variable plant-herbivore interaction.

Local adaptation of parasites to their hosts due to coevolution is a central prediction of many theories in evolutionary biology. However, empirical studies looking for parasite local adaptation show great variation in outcomes, and the reasons for such variation are largely unknown. In a previous study, we showed adaptive differentiation in the arctiid moth Utetheisa ornatrix to its host plant, the pyrrolizidine alkaloid-bearing legume Crotalaria pallida, at the continental scale, but found no differentiation at the regional scale. In the present study, we sampled the same sites to investigate factors that may contribute to the lack of differentiation at the regional scale. We performed field observations that show that specialist and non-specialist polyphagous herbivore incidence varies among populations at both scales. With a series of common-garden experiments we show that some plant traits that may affect herbivory (pyrrolizidine alkaloids and extrafloral nectaries) vary at the regional scale, while other traits (trichomes and nitrogen content) just vary at the continental scale. These results, combined with our previous evidence for plant population differentiation based on larval performance on fresh fruits, suggest that U. ornatrix is subjected to divergent selection even at the regional scale. Finally, with a microsatellite study we investigated population structure of U. ornatrix. We found that population structure is not stable over time: we found population differentiation at the regional scale in the first year of sampling, but not in the second year. Unstable population structure of the herbivore is the most likely cause of the lack of regional adaptation.

Role of methylotrophy during symbiosis between Methylobacterium nodulans and Crotalaria podocarpa.

Some rare leguminous plants of the genus Crotalaria are specifically nodulated by the methylotrophic bacterium Methylobacterium nodulans. In this study, the expression and role of bacterial methylotrophy were investigated during symbiosis between M. nodulans, strain ORS 2060T, and its host legume, Crotalaria podocarpa. Using lacZ fusion to the mxaF gene, we showed that the methylotroph genes are expressed in the root nodules, suggesting methylotrophic activity during symbiosis. In addition, loss of the bacterial methylotrophic function significantly affected plant development. Indeed, inoculation of M. nodulans nonmethylotroph mutants in C. podocarpa decreased the total root nodule number per plant up to 60%, decreased the whole-plant nitrogen fixation capacity up to 42%, and reduced the total dry plant biomass up to 46% compared with the wild-type strain. In contrast, inoculation of the legume C. podocarpa with nonmethylotrophic mutants complemented with functional mxa genes restored the symbiotic wild phenotype. These results demonstrate the key role of methylotrophy during symbiosis between M. nodulans and C. podocarpa.