J. G. C. da Costa

POTASSIUM-USE EFFICIENCY IN COMMON BEAN GENOTYPES

Potassium (K) is one of the most important nutrients limiting yield of common bean in South America. Use of K-efficient crop genotypes along with K fertilizer may be a viable strategy to improve yield and reduce cost of production. A greenhouse experiment was conducted to evaluate K-use efficiency of 10 promising genotypes of common bean (Phaseolus vulgaris L.). The genotypes were grown on an Oxisol at 0 mg K kg−1 (low K) and 200 mg K kg−1 (high K) of soil. Shoot dry weight, grain yield, number of pods, number of grains, 100-grain weight, grain harvest index, and K harvest index were significantly (P < 0.01) affected by level of K as well as genotype, except for the number of pods by genotype. Significant genotypic differences in K-use efficiency were found. On the basis of K-use efficiency (mg grain weight/mg K accumulated in shoot and grain), genotypes were classified as efficient and responsive (ER), efficient and nonresponsive (ENR), nonefficient and responsive (NER), and non-efficient and non-responsive (NENR). Only genotype Diamante Negro was only classified as ER, and genotypes Carioca, Pérola, Rosinha G-2, and Xamego were classified as ENR. Genotypes LM93300166 and LM93300176 were in the group NER, and in the NENR group were genotypes Iraí, Jalo Precoce, and Novo Jalo. From a practical point of view, genotypes which produce high grain yield at a low level of K and respond well to added K are the most desirable because they are able to express their high yield potential in a wide range of K availability.

Evaluation of common bean genotypes for phosphorus use efficiency

Abstract A greenhouse experiment was conducted to evaluate phosphorus (P)‐use efficiency of 10 promising genotypes of common bean (Phaseoius vulgaris L.) with short and normal growth duration. The genotypes were grown on an Oxisol at 25 mg P kg‐1 (low P) and 150 mg P kg‐1 (high P) of soil. Shoot and root dry weight, root length, P concentration in the shoot, and P uptake in the shoot were significantly (P<0.01) affected by soil P concentration and genotype. However, P level did not effect root length and genotype had no effect on root dry weight. On the basis of P‐use efficiency (mg dry weight of shoot/mg P accumulated in the shoot) genotypes were classified as efficient and responsive (ER), efficient and nonresponsive (ENR), nonefficient and responsive (NER), and nonefficient and nonresponsive (NENR). From a practical point of view, genotypes which produce a lot of dry matter in a soil with a low P level, and respond well to added P are the most desirable because they are able to express their high yield potential in a wide range of P environments. Novo Jalo and Pérola genotypes fall into this group. Genotypes Irai, Jalo Precoce and L93300166 fall into the ENR group. Genotypes Carioca, Rosinha G‐2, and Xamengo were classified NER, whereas, genotypes L93300176 and Diamante Negro were classified as NENR. There were no differences between short and normal growth duration genotypes in P‐use efficiency.

Identification of stable fly attractant compounds in vinasse, a byproduct of sugarcane–ethanol distillation

The stable fly, Stomoxys calcitrans (Diptera: Muscidae), is a worldwide pest of livestock. Recent outbreaks of stable flies in sugarcane fields in Brazil have become a serious problem for livestock producers. Larvae and pupae found inside sugarcane stems after harvesting may indicate that stable flies use these stems as potential oviposition or larval development sites. Field observations suggest that outbreaks of stable flies are associated with the vinasse and filter cake derived from biomass distillation in sugarcane ethanol production that are used as fertilizers in sugarcane fields. Adult stable flies are attracted to vinasse, which appears to present an ideal larval development site. The primary goal of the present study is to demonstrate the role of vinasse in influencing the sensory physiological and behavioural responses of stable flies, and to identify its associated volatile attractant compounds. Both laboratory and field studies showed that vinasse is extremely attractive to adult stable flies. Chemical analyses of volatiles collected revealed a wide range of carboxylic acids, alcohols, phenols and aldehydes as potential attractant compounds. These newly identified attractants could be used to develop a tool for the attractant‐baited mass trapping of stable flies in order to reduce infestations.