不同类型拌种剂对花生及其根际微生物的影响

拌种处理对于花生一播全苗和稳定高产非常重要.选用不同类型的4种拌种剂即哈茨木霉菌剂(真菌拮抗剂)、甲基托布津(杀真菌剂)、适乐时(杀真菌剂)、好安威(化学杀虫剂)处理花生种子,通过测定花生农艺性状、品质指标、根际土壤微生物动态等来评价其对花生和环境的综合效应.结果表明:1)各种杀菌剂拌种均能提高花生成苗率,而好安威略差;各拌种剂促进花生株高、叶绿素含量,而单株叶片数适乐时增多,好安威减少,单株分枝数盛花期有所增多(好安威除外),结果期均略减少;单株烂、虫、芽果数均减少,单株秕果数增加,单株饱果数降低(好安威除外),百果重和百仁重提高(哈茨木霉除外),而饱满度降低;最终荚果产量除哈茨木霉略低,其余拌种剂增产效果极显著,甲基托布津、适乐时、好安威比对照分别增产34.58％、25.90％、22.82％.2)哈茨木霉拌种使蛋白质含量、亚油酸含量增幅最大,油份含量增幅较大,油亚比值降幅最大;甲基托布津处理的蛋白质和油份含量降幅最大;适乐时对提高油份含量、油亚比值效果最佳;好安威对品质指标的影响有限.3)从细菌及放线菌与真菌的比值来看,甲基托布津促细菌、抑真菌的效果好且长,对放线菌/真菌比值影响较小;哈茨木霉在前中期促细菌与放线菌、抑真菌的效果明显,但后期效果趋反;适乐时促细菌、抑真菌的效果短促,且一直强烈抑制放线菌;而好安威相比影响较小.4)好安威对根瘤菌具有显著的抑制作用,而哈茨木霉、适乐时、甲基托布津均极显著增加根瘤数量.结论:各拌种剂对花生产量、品质、根瘤、根际微生物产生了较大差异的综合效应,须因地、因时选用;化学杀菌剂甲基托布津的农艺效应、环境微生物效应均最好,唯蛋白质含量、油份含量略有降低,是一种较理想的综合优良拌种剂.     

Effect of high air and soil temperature on dry matter production,pod yield and yield components of groundnut

Groundnuts (Arachis hypogaea L.) grown in the semi-arid tropics are commonly exposed to air and soil temperatures above 35 °C during the reproductive period causing significant yield losses. The objectives of this study were to determine: (i) whether effects of high air and/or high soil temperature in two contrasting cultivars were similar; (ii) the effects of the timing of imposition of high air and soil temperature; (iii) the effects of high air, high soil and both stresses combined on yield and yield components; and (iv) whether the effects of high air and high soil temperature were additive or multiplicative. Plants were grown at optimum and ambient soil temperature from planting until start of podding at 45 d after planting (DAP) in Experiment 1, and until start of flowering at 28 DAP in Experiment 2. Thereafter, plants of each cultivar were exposed to a factorial combination of two air temperatures (optimum: 28°/22 °C and high: 38°/22 °C) and two soil temperatures (ambient: 26°/24 °C and high: 38°/30 °C) until final harvest at 90 DAP. The effects of high air and high soil temperatures imposed from start of flowering or podding were similar. Exposure to high air and/or high soil temperature significantly reduced total dry matter production, partitioning of dry matter to pods, and pod yields in both the cultivars. High air temperature had no significant effect on total flower production but significantly reduced the proportion of flowers setting pegs (fruit-set) and hence fruit numbers. In contrast, high soil temperature significantly reduced flower production, the proportion of pegs forming pods and 100 seed weight. The effects of high air and soil temperature were mostly additive and without interaction. This revised version was published online in June 2006 with corrections to the Cover Date.     

A variant of the satellite RNA of groundnut rosette virus that induces brilliant yellow blotch mosaic symptoms in Nicotiana benthamiana

Some Malawian cultures of groundnut rosette virus (GRV) give rise to variants that, although still causing symptoms of the chlorotic type of rosette in groundnut, induce brilliant yellow blotch mosaic symptoms, instead of the usual veinal chlorosis and mild mottle, in Nicotiana benthamiana. One such isolate (YB) induced the formation in infected plants of a 0.9 kbp dsRNA having extensive sequence homology with molecules of similar size in other naturally occurring isolates of GRV. These dsRNA molecules were shown to be double-stranded forms of single-stranded satellite RNA molecules. Experiments in which the satellite was removed from and restored to isolate YB, or exchanged with those from other GRV isolates, showed that it carries the determinant for yellow blotch mosaic symptoms. Plants inoculated with the 0.9 kbp dsRNA (denatured or undenatured) developed yellow blotch mosaic even when the satellite-free GRV helper was not inoculated until 11 days later. The satellite RNA is therefore a very stable molecule. Prior infection of N. benthamiana with a GRV isolate containing a normal form of the satellite protected against expression of yellow blotch mosaic symptoms when the plants were later inoculated with isolate YB, whereas prior infection with satellite-free isolates did not. This provides a simple method of determining whether a GRV isolate has an associated satellite RNA. The YB satellite seems to be a newly recognised variant additional to those known to cause the chlorotic, green and other forms of groundnut rosette disease.     

Thidiazuron-induced highly morphogenic callus and high frequency regeneration of fertile peanut (Arachis hypogaea L.) plants

Summary An efficient regeneration system was developed by culturing immature cotyledons and embryo axes of Arachis hypogaea L. cv. Georgia Green on Murashige and Skoog basal medium (MS) supplemented with various concentrations of thidiazuron (TDZ; 1, 5, 10, and 15 μM). Highly morphogenic callus was produced from 100% of the explants comprising the cotyledon with attached embryo axis when cultured in the dark on 10 μM TDZ. Upon excision and continued culture in the dark on 10 μM TDZ, morphogenic callus grew repetitively during monthly subcultures and retained its regeneration potential. For organogenesis, a gradual reduction in TDZ concentration and exposure to light were necessary before transfer to MS basal medium. Inclusion of indole-3-butyric acid in liquid MS medium favored rooting of recovered shoots. A distinct feature of this investigation is the induction of highly morphogenic callus by TDZ and regeneration of morphologically normal, fertile peanut plants after 8 months of callus subculture.     

Resistance in groundnut (Arachis hypogaea L.) to Aphis craccivora (Koch).

The behaviour, development and reproductive capacity of Aphis craccivora, vector of a number of groundnut viruses, are compared on a range of susceptible and resistant genotypes. Field trials demonstrated no significant difference between genotypes in the rate of arrival of alates, but population development was slower, and subsequent population decline faster, on the genotype EC 36892 (ICG 5240). Behavioural studies in the screenhouse, likewise showed no inhibition to alighting onto EC 36892 though choice tests demonstrated a significant redistribution of the population in favour of the susceptible genotype TMV 2 (ICG 221) over the following 10 h. In clip cage experiments, development was faster and nymphal numbers were higher on the genotype TMV 2 compared to EC 36892.     

Efficacy of Milsana®, a Formulated Plant Extract from Reynoutria sachalinensis, against Powdery Mildew of Tomato (Leveillula taurica)

The efficacy of Milsana^® VP 1999 and 2000 (a formulated plant extract of Reynoutria sachalinensis), known to induce resistance to powdery mildew on cucumbers, was tested against Leveillula taurica (Lév.) Arn. on greenhouse tomato. In four out of five trials, Milsana^® achieved a disease reduction ranging from 42.2 to 64.6%. In one trial only, its efficacy was exceptionally low (23%). Application rates and disease pressure proved to be the main factors affecting the level of control. Milsana^® was significantly less effective than fungicides (alternated DMIs and penconazole) in situ. In contrast, Milsana^® was equally effective to wettable sulphur indicating that its effect was rather preventive than curative. The level of efficacy achieved by either Milsana^® or fungicides did not result in a significant increase of yield. Laboratory tests showed that Milsana^® (VP 1999) had a direct effect on conidial germination. Whether this effect significantly contributes to its field efficacy, remains to be elucidated. Overall, results indicate that Milsana^® could play an important role in disease management of powdery mildew in organic and low input tomato production.     

Differences in yield determining processes of groundnut (Arachis hypogaea L.) genotypes in varied drought environments1

Thirty-six groundnut gentoypes of varied origin were evaluated for their yield, crop growth rates (C), and partitioning to reproductive sinks (p) in three trials. In the trials irrigation and sowing date were used to vary the amount of water available either throughout the crops' life, or through the grain filling phase. Genotype performance across the five environments for these attributes showed that although differences in C existed, differences in the stability of the partitioning were the dominant attribute of genotypes adapted to the drought prone Sahelian region. Data suggested that these differences were more attributable to tolerance to temperature and/or humidity than water stress. Over all treatments canopy temperatures relative to air (CATD) were strongly correlated with the C observed, but not so with yield; and differences between genotypes in the relationship between C and CATD were not statistically significant.     

Effects of Bradyrhizobium strain and host genotype,nodule dry weight and leaf area on groundnut (Arachis hypogaea L. ssp. fastigiata) yield

Effects of inoculating four Arachis hypogaea ssp. fastigiata cultivars with 17 Bradyrhizobium spp. strains were studied in a glasshouse experiment using a sandy soil devoid of an indigenous Bradyrhizobium population. Firstly, a wide range of parameters, indicative of symbiotic performance, were assessed for their influence on seed yield, by correlation and statistical analyses. It was found that nodule dry weight and leaf area were relevant parameters concerning seed yield. Secondly, the effects of host and strain genotype on those parameters were described.Variations in nodule dry weight did not have an effect on seed yield, except for cultivar Natal Common at lower nodule dry weight values. Therefore, it was concluded that the quantity of nitrogen fixing tissue met the demand for combined nitrogen and did not limit seed yield. This conclusion was further supported by the observation that at low nodule numbers per plant the nodule size increased to generate sufficient nitrogen fixing tissue.Leaf area, which comprises components for both photosynthetic capacity and plant development, was found to correlate well with seed yield. An increase in leaf area resulted in significant seed yield increases for all three spanish-type cultivars, but not for the valencia-type cultivar. Leaf area, thus, appeared as a factor limiting seed yield of spanish-type groundnuts.Cultivar performance concerning seed yield was significantly better for Natal Common compared to the other three cultivars, while Natal Common had a significantly lower plant (biomass excluding seed) dry weight value.Inoculation with different strains of Bradyrhizobium resulted in significantly different nodule dry weight values, but hardly led to significant differences in seed yield. This agreed with the finding that the amount of nitrogen fixing tissue appeared not to limit the availability of combined nitrogen.A large quantity of nitrogen was partitioned to the groundnut seeds: 62% to 76% of total accumulated nitrogen was located in the seeds.This study showed that testing for symbiotic effectiveness in the groundnut Bradyrhizobium symbiosis should include assessment of final (seed and biomass) yield, because parameters measured at stages prior to maturity, like nodulation parameters, may lead to flawed effectiveness ratings.