Morphophysiological characteristics of Brazilian bean genotypes related with sulfentrazone tolerance.

In the bean crop there are limited options of herbicides to control eudicotyledons weeds in pre-emergence and sulfentrazone presents potential to be used in a weed management program. The aim of this study was to determine the tolerance of a large number of Brazilian bean genotypes to sulfentrazone and their relation with morphophysiological characteristics, associating it to market classes, seed size and their center of origin. It was evaluated the effect of sulfentrazone application (400 g a.i. ha-1) in pre-emergence of 40 Brazilian bean genotypes, 36 of which were common-bean (Phaseolus vulgaris), two cowpeas (Vigna unguiculata), one adzuki bean (Vigna angularis) and one mung bean (Vigna radiata). There was high tolerance variation of the genotypes to sulfentrazone. Morphological parameters were strongly related with relative tolerance. Common bean genotypes that had medium to large seed size (cranberry and carioca) were more tolerant, while small-sized seed genotypes were more sensitive (black). Andean genotypes were more tolerant than Mesoamerican genotypes. Within the Mesoamerican group, medium-sized seed genotypes (carioca beans) were more tolerant than small-sized seed (black beans). Considering only the Vigna genera, cowpea was highly tolerant to sulfentrazone, while mung bean showed intermediary response and adzuki bean was completely sensible.

Influence of temperature on the retention, absorption and translocation of fomesafen and imazamox in Euphorbia heterophylla.

Climate change will be an additional issue to the challenge to manage herbicide resistant weeds. This work investigated the impact of three temperature regimes (10/5, 20/15 and 30/25 °C) on the efficacy, foliar retention, absorption and translocation of fomesafen, protoporphyrinogen oxidase (PPO) inhibitor, and imazamox, acetolactate synthase (ALS) inhibitor, between two Euphorbia heterophylla populations, one susceptible (S) and one multiple PPO and ALS resistant (R). The R population went from 5 (fomesafen) and 12 (imazamox) times more resistant than the S population at 10/5 °C to more than 100 times to both herbicides at 20/15 and 30/25 °C. Leaf retention of fomesafen was not affected by temperature; however, imazamox retention was less at 10/5 and 20/15 °C than at 30/25 °C, and the R population always retained less imazamox than the S population. 14C-fomesafen absorption was similar between populations, but lower amounts were absorbed at 10/5 °C regardless of the evaluation time. Recovered 14C-imazamox rates decreased in both populations as the evaluation time increased, ranging from 82 to 92% at 6 h after treatment (HAT), and from 47 to 76% at 48 HAT, depending on the temperature regime. The 14C-imazamox losses were greater from 24 HAT in R plants grown at 30/25 °C and in all temperature regimes at 48 HAT. Although both populations translocated large amounts of imazamox, the S population distributed it in the rest of the plant (33%) and roots (15%), while the R population kept it mainly on the treated leaf (24%) or lost ~20% more herbicide than S population at 48 HAT, indicating the need for further studies on root exudation between these populations. Low temperatures reduced resistance levels to fomesafen and imazamox in E. heterophylla, suggesting that temperature influences the expression of the mechanisms that govern this multiple resistance.