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851.
Rice (Oryza sativa L.) yield is severely reduced by the brown planthopper (BPH), Nilaparvata lugens Stål, in Asian countries. Increasing resistance in rice against BPH can mitigate yield loss. Previous reports indicated the presence of three BPH resistance genes, BPH2, BPH17-ptb, and BPH32, in durable resistant indica rice cultivar ‘PTB33’. However, several important questions remain unclear; the genetic locations of BPH resistance genes on rice chromosomes and how these genes confer resistance, especially with relationship to three major categories of resistance mechanisms; antibiosis, antixenosis or tolerance. In this study, locations of BPH2, BPH17-ptb, and BPH32 were delimited using chromosome segment substitution lines derived from crosses between ‘Taichung 65’ and near-isogenic lines for BPH2 (BPH2-NIL), BPH17-ptb (BPH17-ptb-NIL), and BPH32 (BPH32-NIL). BPH2 was delimited as approximately 247.5 kbp between RM28449 and ID-161-2 on chromosome 12. BPH17-ptb and BPH32 were located between RM1305 and RM6156 on chromosome 4 and RM508 and RM19341 on chromosome 6, respectively. The antibiosis, antixenosis, and tolerance were estimated by several tests using BPH2-NIL, BPH17-ptb-NIL, and BPH32-NIL. BPH2 and BPH17-ptb showed resistance to antibiosis and antixenosis, while BPH17-ptb and BPH32 showed tolerance. These results contribute to the development of durable BPH resistance lines using three resistance genes from ‘PTB33’.  相似文献   
852.
Liming is one of the key agronomic practices to improve crop yields in acid soils because, among other things, it reduces aluminum toxicity and creates favorable conditions for crop growth. For an effective liming program, the methods to determine lime requirement should be as precise as possible. This paper reviews the existing lime requirement methods and discusses the potential of a new one suitable for routine use in the laboratory to test most agricultural soils. The most widely used lime requirement methods can be categorized into four groups: titration, incubation, buffer, and field methods. Other methods such as spectroscopy method or the use of empirical equations have also been adopted. Although some methods are highly reliable, they are not optimal for routine use because they are inconvenient during the laboratory procedures or cannot be validated for all conditions. Based on the linearity between soil pH and the added base in the pH range from 4.5–6.5 in most agricultural soils, a titration-based method on 1:1 soil:0.01 M CaCl2 slurry of a single sample appears to be a promising candidate for routine use. In further studies, this generally applicable method should be evaluated to provide a better comparison to established methods for lime requirement determination.  相似文献   
853.

Shrimp aquaculture is the biggest source of export income in Vietnam. However, the development of the shrimp poses a serious threat to coastal mangroves by converting coastal mangroves into shrimp farms. Much effort has been made to replant mangroves and reduce the impacts of shrimp farming on the environment, and maintaining mangrove coverage at 30–50% of total farm area has provided the highest benefits in the integrated mangrove shrimp model. In this study, we re-examine the benefits of forest cover on the survival and yield of tiger shrimp (Penaeus monodon) in the integrated mangrove shrimp farming systems in Ca Mau province, Vietnam. The study found positive linear correlations of log transformed survival and yield of tiger shrimp with forest cover of the forms: Ln (survival)?=????1.39?+?0.038?×?forest coverage (r2?=?0.22; p value?=?0.0007); Ln (yield)?=?3.55?+?0.026?×?forest coverage (r2?=?0.16; p value?=?0.004). The households with high forest cover (i.e.,?>?45%) also had 1.07?±?0.29 and 1.39?±?0.36 (CI 95%, p value?=?0.000) kg ha?1 higher yield per night harvest than those with medium and low forest cover, respectively. As a result, households with high forest cover have higher benefits than those with lower forest cover. Our findings together with previous published studies lead to the recommendation that farmers maintain mangroves in farming systems for better economic and environmental benefits.

  相似文献   
854.
The aim of this study was to evaluate the effects of dietary soluble non-starch polysaccharide (sNSP) content and xylanase supplementation on production performance, egg quality parameters, and nutrient digestibility in Hy-line Brown layers from 25 to 32 wk of age. A total of 144 Hy-line Brown laying hens (25 wk of age) were randomly allocated to 1 of 4 wheat-based dietary treatments in a 2 × 2 factorial experimental design, with 36 replicates of individual hens per treatment. The diets were formulated to contain either a high or low sNSP level (at 13.3 or 10.8 g/kg) and were supplemented with either 0 or 12,000 BXU/kg exogenous xylanase. Birds were fed these treatment diets for an 8-wk period, and hen production performance, including daily egg production, average egg weight, daily egg mass, feed conversion ratio and proportion of dirty and abnormal eggs were measured at bird age 25 to 28 wk and 29 to 32 wk. An interaction between sNSP content of the diet and xylanase supplementation was observed on daily egg production from 25 to 28 wk of age (P = 0.018); birds fed the high sNSP diet without xylanase had lower egg production than those fed any other treatment. An interaction between the 2 dietary factors was also observed on hen weight gain at 29 to 32 wk of age (P = 0.014), with birds fed the low sNSP diet with 12,000 BXU/kg xylanase presenting greater weight gain compared to those fed the high sNSP diet with 12,000 BXU/kg xylanase. Feed intake at 29 to 32 wk of age was reduced by xylanase supplementation (P = 0.047). Xylanase supplementation also increased yolk colour score at both 28 and 32 wk of age, and decreased yolk weight at 32 wk of age (P = 0.014, 0.037 and 0.013, respectively). Birds fed the low sNSP diet presented lower protein digestibility (P = 0.024) than those fed the high sNSP diet. Additionally, birds fed high sNSP presented higher shell reflectivity at both 28 and 32 wk of age (P = 0.05 and 0.036, respectively). The influence of duration of feeding the treatment diets on egg quality was also determined. It was observed that egg weight, yolk weight and yolk colour score consistently increased over time, regardless of experimental treatment effects. In contrast, Haugh Unit and albumen height significantly decreased throughout the study period in all treatments, although this was less pronounced in hens fed the treatment with high sNSP and no supplemental xylanase. A reduction in shell breaking strength over time was observed only in hens fed the treatments without xylanase addition, and shell thickness was improved over time only in birds fed the low sNSP diet with xylanase. The impacts of the dietary treatments were largely inconsistent in this study, so a solid conclusion cannot be drawn. However, these findings do indicate that dietary NSP level influences layer production performance, and thus should be considered when formulating laying hen diets. It also proved that further research is warranted into how to optimize the benefits of xylanase application in laying hens.  相似文献   
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