Genes controlling seed dormancy and pre-harvest sprouting in a rice-wheat-barley comparison

Pre-harvest sprouting results in significant economic loss for the grain industry around the world. Lack of adequate seed dormancy is the major reason for pre-harvest sprouting in the field under wet weather conditions. Although this trait is governed by multiple genes it is also highly heritable. A major QTL controlling both pre-harvest sprouting and seed dormancy has been identified on the long arm of barley chromosome 5H, and it explains over 70% of the phenotypic variation. Comparative genomics approaches among barley, wheat and rice were used to identify candidate gene(s) controlling seed dormancy and hence one aspect of pre-harvest sprouting. The barley seed dormancy/pre-harvest sprouting QTL was located in a region that showed good synteny with the terminal end of the long arm of rice chromosome 3. The rice DNA sequences were annotated and a gene encoding GA20-oxidase was identified as a candidate gene controlling the seed dormancy/pre-harvest sprouting QTL on 5HL. This chromosomal region also shared synteny with the telomere region of wheat chromosome 4AL, but was located outside of the QTL reported for seed dormancy in wheat. The wheat chromosome 4AL QTL region for seed dormancy was syntenic to both rice chromosome 3 and 11. In both cases, corresponding QTLs for seed dormancy have been mapped in rice.C. Li and P. Ni contributed equally to this work     

Genetic basis of pre-harvest sprouting tolerance using single-locus and two-locus QTL analyses in bread wheat

Quantitative trait loci (QTL) analysis for pre-harvest sprouting tolerance (PHST) in bread wheat was conducted following single-locus and two-locus analyses, using data on a set of 110 recombinant inbred lines (RILs) of the International Triticeae Mapping Initiative population grown in four different environments. Single-locus analysis following composite interval mapping (CIM) resolved a total of five QTLs with one to four QTLs in each of the four individual environments. Four of these five QTLs were also detected following two-locus analysis, which resolved a total of 14 QTLs including 8 main effect QTLs (M-QTLs), 8 epistatic QTLs (E-QTLs) and 5 QTLs involved in QTL × environment (QE) or QTL × QTL × environment (QQE) interactions, some of these QTLs being common. The analysis revealed that a major fraction (76.68%) of the total phenotypic variation explained for PHST is due to M-QTLs (47.95%) and E-QTLs (28.73%), and that only a very small fraction of variation (3.24%) is due to QE and QQE interactions. Thus, more than three-quarters of the genetic variation for PHST is fixable and would contribute directly to gains under selection. Two QTLs that were detected in more than one environment and at LOD scores above the threshold values were located on 3BL and 3DL presumably in the vicinity of the dormancy gene TaVp1. Another QTL was found to be located on 3B, perhaps in close proximity to the R gene for red grain colour. However, these associations of QTLs for PHST with genes for dormancy and grain colour are only suggestive. The results obtained in the present study suggest that PHST is a complex trait controlled by large number of QTLs, some of them interacting among themselves or with the environment. These QTLs can be brought together through marker-aided selection, leading to enhanced PHST.     

A new PCR-based marker on chromosome 4AL for resistance to pre-harvest sprouting in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Pre-harvest sprouting (PHS) is a complex trait controlled by multiple genes with strong interaction between environment and genotype that makes it difficult to select breeding materials by phenotypic assessment. One of the most important genes for pre-harvest sprouting resistance is consistently identified on the long arm of chromosome 4A. The 4AL PHS tolerance gene has therefore been targeted by Australian white-grained wheat breeders. A new robust PCR marker for the PHS QTL on wheat chromosome 4AL based on candidate genes search was developed in this study. The new marker was mapped on 4AL deletion bin 13-0.59-0.66 using 4AL deletion lines derived from Chinese Spring. This marker is located on 4AL between molecular markers Xbarc170 and Xwg622 in the doubled-haploid wheat population Cranbrook × Halberd. It was mapped between molecular markers Xbarc170 and Xgwm269 that have been previously shown to be closely linked to grain dormancy in the doubled haploid wheat population SW95-50213 × Cunningham and was co-located with Xgwm269 in population Janz × AUS1408. This marker offers an additional efficient tool for marker-assisted selection of dormancy for white-grained wheat breeding. Comparative analysis indicated that the wheat chromosome 4AL QTL for seed dormancy and PHS resistance is homologous with the barley QTL on chromosome 5HL controlling seed dormancy and PHS resistance. This marker will facilitate identification of the gene associated with the 4A QTL that controls a major component of grain dormancy and PHS resistance.     

Enhancement of the biocontrol agent Candida oleophila (strain O) survival and control efficiency under extreme conditions of water activity and relative humidity

The objective of this work is to evaluate the ability of some additive substances in protecting the biocontrol agent Candida oleophila (strain O) against the adverse effects of environmental factors, such as water activity (a_w, 0.93 and 0.98) and relative humidity (75% and 98%). The protection obtained with various protectant substances, skimmed milk (SM), peptone, maltose, sucrose, sorbitol, lactose and polyethylene glycol was assayed under in vitro and in vivo conditions. The yeast cells with the highest level of protecting agents (1%) had higher viability than those with low protectant levels (0.1% and 0.5%). SM, sucrose and sorbitol improved significantly the C. oleophila survival on apple fruit surface by 80.8%, 42.26% and 37.27% and gave a significant protection (from 96% to 100%) against Penicillium expansum under dried conditions. The highest strain O density and efficacy was obtained with SM. Under experimental conditions reflecting practical conditions, SM applied in combination with the strain O resulted in improved biocontrol efficacy by 74.65%. Therefore, SM could be used as material substrate with the best sugar protectants during the formulation process of this antagonistic yeast for eventual pre-harvest application.     

小麦抗穗发芽研究进展

穗发芽严重影响小麦品质和产量。种子自身休眠特性、α-淀粉酶活性、α-淀粉酶抑制剂、迟熟α-淀粉酶活性、种皮颜色、颖壳抑制物以及穗部形态等,均是影响小麦穗发芽的重要因素,其中对子粒休眠特性和α-淀粉酶活性的研究较为深入。位于第3染色体组上的R基因、休眠基因以及4AL上的Phs基因均与小麦穗发芽密切相关。已开发出一些与穗发芽抗性相关的分子标记,其中位于第3部分同源群的三重R基因和位于3B染色体的STS标记Vp1B3,以及位于3A染色体的主效QTL位点QPhs.ccsu-3A.1均可直接用于穗发芽抗性的筛选。本文对以上内容进行了详细论述,并就今后如何提高小麦穗发芽抗性进行了讨论。     

黄河中游地区节节麦抗穗发芽的鉴定与分析

小麦穗发芽是小麦生产中的主要灾害和重要问题,在普通小麦中缺乏抗穗发芽的品种资源。本试验通过对35份黄河中游地区节节麦、14份国外节节麦及部分小麦品种的发芽率的测定及抗性多样性分析,综合评价了黄河中游地区节节麦的穗发芽抗性状况。结果表明,节节麦穗发芽抗性普遍高于小麦品种,黄河中游地区节节麦的抗穗发芽能力优于国外材料,其中以T005、T007、T008、T016、T030、T062、T065、T068、T069、T072和T085等11个材料的抗穗发芽能力最强,是小麦穗发芽改良优异的抗源材料。     

水稻不同品种的穗发芽及其对外源激素的反应

选择8份早籼稻品种在开花后不同天数取穗子进行保湿培养,观察其抗穗发芽能力的差异。结果显示不同品种之间的抗穗发芽能力存在较大差异;处理以开花后22d左右的穗子保湿培养6d考查穗发芽,就能较好地比较出品种之间的差异。以3种不同浓度的赤霉素(GA3)和脱落酸(ABA)进行溶液培养,30mg／kg的赤霉素有明显促进穗发芽的效果,脱落酸抑制穗发芽的效果在不同品种之间表现出比较大的差异。     

Trichoderma/pathogen/plant interaction in pre-harvest food security

Large losses before crop harvesting are caused by plant pathogens, such as viruses, bacteria, oomycetes, fungi, and nematodes. Among these, fungi are the major cause of losses in agriculture worldwide. Plant pathogens are still controlled through application of agrochemicals, causing human disease and impacting environmental and food security. Biological control provides a safe alternative for the control of fungal plant pathogens, because of the ability of biocontrol agents to establish in the ecosystem. Some Trichoderma spp. are considered potential agents in the control of fungal plant diseases. They can interact directly with roots, increasing plant growth, resistance to diseases, and tolerance to abiotic stress. Furthermore, Trichoderma can directly kill fungal plant pathogens by antibiosis, as well as via mycoparasitism strategies. In this review, we will discuss the interactions between Trichoderma/fungal pathogens/plants during the pre-harvest of crops. In addition, we will highlight how these interactions can influence crop production and food security. Finally, we will describe the future of crop production using antimicrobial peptides, plants carrying pathogen-derived resistance, and plantibodies.