Screening of antagonistic bacteria for biological control of nursery wilt of black pepper (Piper nigrum)

Bacterial antagonists of Phytophthora capsici were isolated from underground shoot portions of rooted cuttings of black pepper. Initially isolates were screened by dual culture on potato dextrose agar and carrot agar. Further, a screening was done on black pepper shoots for supression of lesion caused by the pathogen. Most of the antagonists showed varying levels of antagonism in the dual culture and the shoot assay. Isolate PN-026, showing the highest suppression of lesion development in the shoot assay was found to be the most efficient antagonist in reducing Phytophthora capsici induced nursery wilt of black pepper. This screening involving the host, pathogen, and the antagonist, performed on black pepper shoot (the planting material for this vegetatively propagated crop), could be used as a rapid and reliable method for the isolation of efficient bacterial antagonists of P. capsici.     

Cloning and functional annotation of rare mRNA species from drought-stressed hot pepper (<Emphasis Type="Italic">Capsicum annuum</Emphasis>)

To better understand gene expression at very low levels, we have designed a method to eliminate cDNA clones representing abundant mRNAs. A cDNA library for drought-stressed hot pepper (Capsicum annuum) (Choi et al., 2002) underwent double-negative screening, once with probes made from a drought-stressed plant, the second time, with probes from a non-stressed plant. The cDNA clones that showed very weak or negative signals were isolated for further analysis, which resulted in 1399 cDNA clones from about 20,000 screened clones. When nucleotide sequences were determined, we obtained 1142 tentative unique genes, with a redundancy rate of 20.41%. An homology database search for the deduced amino acid sequences revealed that about 79% of the cDNA clones could not be matched for functioning with previously characterized sequences. However, when these uncategorized clones were subjected to classification based on functional domains, most could be cited. Notably, clones with possible functions in RNA transport, protein synthesis, and regulation of protein activity showed a dramatic increase in appearance while those coding for transposable elements, viral proteins, and plasmid proteins occupied a much smaller portion compared with those in theArabidopsis thaliana genome. In addition, those coding for proteins targeted to the endoplasmic reticulum were dramatically more abundant in our clones compared with theArabidopsis database.     

Growth, photosynthesis and chlorophyll fluorescence of sweet pepper plants as affected by the cultivation method

Different methods of sweet pepper cultivation (organic, integrated and conventional farming) were evaluated under greenhouse conditions. Organic treatment was defined as only 4‐kg manure application at the preplanting stage. Conventional and integrated treatments consisted of application of the manure dosage plus chemical fertiliser at 100% and 50% of the local farmers’ amount, respectively, to avoid nutrient depletion. Plant growth parameters such as shoot dry matter, total leaf area and leaf weight fraction were all reduced in the organic treatment compared with the conventional. Leaf expansion was dramatically reduced in the organic treatment 155 days after transplanting. Relative growth rates were significantly affected by the nitrogen concentration in each organ and were directly related to the cultivation method. Chlorophylls (a + b) contents in the leaves were reduced in the organic treatment and were directly correlated with the nondestructive quantification of chlorophylls using a portable chlorophyll meter. Net photosynthesis was also reduced in the organic treatment, but chlorophyll fluorescence was not affected. This study shows that biometric monitoring and fast and non‐invasive techniques of plant nutrient status analysis could help to improve growth as easy and useful tools to follow the nutrient status at different phenological stages, especially when no chemical fertilisers are applied.     

Differential expression of root-knot nematode resistance genes in tomato and pepper: evidence with Meloidogyne incognita virulent and avirulent near-isogenic lineages

Reproduction of artificially selected near isogenic Meloidogyne incognita lineages virulent and avirulent against the Mi resistance gene of tomato was assessed on host and resistant lines and cultivars of pepper. Egg mass production following inoculation of individual potted seedlings with second-stage juveniles was studied in experiments conducted in controlled environment. Artificially selected Mi-virulent nematode populations were unable to develop on resistant pepper lines PM 217 and PM 687. This suggests that the genetic systems governing resistance to root-knot nematodes are differently expressed in tomato and pepper, in spite of the very close phylogenetic relationships and structural genomic homologies occurring between these two vegetable crops. Moreover, these artificially selected nematode populations were also found unable to develop on the susceptible pepper cultivars California Wonder and Doux Long des Landes, while their pathogenicity was not significantly affected on susceptible tomatoes. Due to the existence of naturally virulent Meloidogyne populations, these results enhance the need for a better understanding of the mechanisms involved, in order to develop new forms of management of plant resistance to root-knot nematodes.     

A portable electroantennogram sensor for routine measurements of pheromone concentrations in greenhouses

Mating disruption using pheromone dispensers is an emerging insect control method in greenhouses in the Netherlands. For routine measurements of the pheromone level in greenhouses a portable and compact device based on electroantennography (EAG) was developed. The instrument was tested in different greenhouses under varying conditions using antennae of males of the noctuid moth Chrysodeixis chalcites. Relative differences in pheromone concentration between greenhouses loaded with pheromone dispensers and control greenhouses could be measured in a reliable way. Changes in pheromone concentration were clearly demonstrated by measurements during the growing season. The advantages of the instrument presented over previously described devices are its true portableness, ease of use and uncomplicated measuring principle. The device can be operated routinely by non-experts, and many measurements can be made in a short period of time. Preliminary outdoor measurements using antennae of male Cydia pomonella as sensor showed the potential of the instrument for use in the open field. The portable EAG sensor described here may provide a practical means for monitoring pheromone concentration and dispersal from dispensers applied for mating disruption.     

辣椒锌指蛋白DnaJ-Like基因家族鉴定及对高温胁迫的表达响应

植物DnaJ-Like锌指蛋白（DNAJE）是近年来发现的一类具有重要功能的蛋白,在光合作用、质体发育与运动和植物抗逆及防御反应中发挥重要作用。基于辣椒全基因组数据,对辣椒DNAJE基因家族（CaDNAJE）进行鉴定,利用生物信息学方法对基因和蛋白特征、比较进化、共线性关系及高温胁迫下基因表达模式等进行分析。结果表明,CaDNAJE基因家族有28个成员,不均匀的分布在10条染色体和3个Scaffold上,氨基酸序列长度为99-470 aa,分子量为10.05-52.26 kD,理论等电点（pI）为4.75-9.64,其编码蛋白主要定位在叶绿体和细胞核中;辣椒、番茄和拟南芥的比较进化分析可将其分为GroupⅠ 和GroupⅡ 2个亚族,同一亚族具有类似的蛋白保守motif和基因结构;CaDNAJE基因启动子区包含大量光响应、激素响应和胁迫应答元件;辣椒与拟南芥DNAJE之间存在10对共线性基因,辣椒种内仅有1对;辣椒不同组织转录组分析发现,GroupⅠ 中多数成员在各组织中均有高表达,而GroupⅡ 中除CaDNAJE2、CaDNAJE9等基因存在高表达外,多数基因表达量都很低甚至不表达;高温胁迫下,辣椒叶片过氧化氢含量急速上升后降低,丙二醛含量持续升高,抗氧化物酶活性也有不同程度的提高。同时,高温诱导热激转录因子Hsf和热激蛋白HSP耐热相关基因及CaDNAJE基因高表达,在不同胁迫时期发挥调控作用。推测CaDNAJE基因家族可能参与辣椒响应高温胁迫,提高其耐受力,以降低细胞损伤。     

辣椒连作对土壤细菌群落的影响

【目的】土壤微生物对农业生态系统的长期可持续性至关重要。为探讨不同连作年限对辣椒土壤细菌群落结构和潜在功能的影响。【方法】采用16S rRNA基因高通量测序PICRUSt功能预测相结合的研究方法,对不同连作年限下(1Y、3Y、5Y和10Y)的辣椒土壤细菌微生物群落结构和功能进行分析。【结果】微生物多样性指数和共生网络复杂度随连作年限的延长而降低,同时,连作年限变化对细菌群落组成有显著影响。不同的土壤细菌种群对连作措施的响应程度不一,长期连作增加了变形菌门和拟杆菌门的相对丰度,但降低了绿弯菌门、酸杆菌门、厚壁菌门和髌骨细菌门的相对丰度。PICRUSt功能预测结果表明,延长连作年限改变了土壤细菌整体的氮、磷代谢能力,导致细菌群预测功能基因发生了变化,能量代谢、氨基酸代谢和碳水化合物代谢等重要代谢功能基因减少,而折叠、分类和降解、复制和修复、膜转运、细胞生长与死亡等功能基因丰度明显增加。冗余分析表明,土壤有机质和有效磷是影响细菌群落迁移和功能变化的关键土壤理化因子。【结论】延长辣椒连作年限后,细菌群落结构改变和多样性下降导致土壤微生物群落功能失调可能是造成辣椒连作障碍的原因之一。     

Effect of pollination on carbohydrate metabolism,in young fruits of Citrullus lanatus and Capsicum annuum

During a 9 day period after anthesis the concentration of reducing sugars showed a 6-fold increase in fruits of Citrullus lanatus, and a 2-fold increase in those of Capsicum annuum. These increases were associated with acid invertase, the specific activity of which was high in ovaries at anthesis and which increased 5-fold in watermelon and 1.5-fold in pepper during the same period. Sucrose synthase apparently plays only a minor role in sucrose hydrolysis. Changes in sugar concentrations and both acid invertase and sucrose synthase activities were similar in fruits developed both after pollination or hormone (NAA) treatment of ovaries. In non-pollinated ovaries of watermelon there was also an increase in invertase activity up to 6 days after anthesis which paralleled the increase in activity in seeded and parthenocarpic fruits. However, there was no increase in either reducing sugars or sucrose, indicating that sucrose is not imported into non-pollinated ovaries. Utilisation of reserve starch may help prolong the life of non-pollinated ovaries for up to one week after anthesis.     

Phenylalanine ammonia-lyase activity and capsaicin-precursor compounds in p-fluorophenylalanine-resistant and -sensitive variant cells of chili pepper (Capsicum annuum)

Cell suspension cultures of chili pepper ( Capsicum annuum L. cv. Tampiqueño 74) displaying differences in their resistance to p -fluorophenylalanine (PFP) and in their contents of capsaicin (the compound which is responsible for the hot taste of chili pepper fruits) were characterized in relation to the activity of phenylalanine ammonia-lyase (PAL; EC 4.3.1.5), the levels of free l -phenylalanine, phenolics and the phenylpropanoid acids involved in capsaicin biosynthesis. A nonselected cell line, a sensitive line (CA-02), a moderately resistant cell line (CA-29) and two resistant cell lines (CA-04 and CA-16) were studied. Higher PAL activities and higher levels of phenylalanine and phenolics were found in the PFP-resistant cells even after a minimum of 9 subcultures (15 days each) in the absence of the analog, indicating that the selected trait was stable. PFP-resistant chili pepper cells accumulated higher amounts of capsaicin precursors (cinnamic, caffeic and ferulic acids) than either the nonselected cells or the sensitive cell line. p -Coumaric acid was not detected at significant levels in any of the cell cultures. Overall, accumulation of free phenyl-alanine correlated well with PAL activity, phenolics, phenylpropanoids and capsaicin levels, suggesting an active flow through the phenylpropanoid pathway in PFP-resistant cells of chili pepper.