Within‐population variation in resistance of Digitaria sanguinalis to Ustilago syntherismae resulting from different modes of seed germination and environment

In annual plants affected by inflorescence‐invading smut pathogens, avoidance of infection is crucial, while in the event of infection, the existence of different degrees of tolerance could also affect the interaction dynamics. Two experiments were performed with Digitaria sanguinalis spikelets vacuum inoculated with ustilospores of Ustilago syntherismae. In the first experiment, they were sown in pots and mature plants were checked to detect internal hyphae. Observations revealed the presence of symptomless mycelium in a few plants. In the second experiment the spikelets, from two different lots, were grown in a chamber. The objective was to explore the importance of two factors in the degree of seedling infection, one genotypic – type of germination (TG; radicular or coleoptilar) and one environmental – 48 h dark treatment (DT) applied just after germination. Analysis of the infection frequency showed that all the main effects (seed lot origin, TG and DT) were significant, while interactions were not. For TG, the estimated least square mean infection percentages were 66% for radicular germination and 46% for coleoptilar germination. Darkness increased seedling infection by 25%. Differences between TG, DT and their relationship with mesocotyl length exposed to the germinating spores are discussed.     

Fungal derived cytokinins are necessary for normal Ustilago maydis infection of maize

Phytohormones derived from fungi play a key role in regulating plant–pathogen interactions; however, deciphering the separate contributions of pathogen and plant during infection has been difficult. Here, the Ustilago maydis–Zea mays pathosystem was used to investigate this chemical exchange. Ustilago maydis, the causative agent of maize smut, produces cytokinins (CK), which are a group of phytohormones responsible for directing plant development. The characteristic symptom of smut disease is the formation of tumours composed of plant and fungal tissue. Isopentenyltransferase (IPT) catalyses the rate‐limiting step in CK biosynthesis, and U. maydis strains in which the sole tRNA‐ipt gene was deleted no longer produced CKs. These deletion strains elicited fewer, smaller tumours than the pathogenic strain SG200. High performance liquid chromatography‐electrospray ionization tandem mass spectrometry (HPLC‐ESI MS/MS) was used to detect and quantify phytohormone levels in infected tissue. This revealed that key hormone changes in SG200 infections were not present in infections by deletion strains, suggesting that CK production by U. maydis is required for the altered phytohormone profile in infected tissue relative to uninfected tissue. Separate analyses indicated that U. maydis tRNA‐ipt mutants might be altered in their ability to metabolize CKs taken up from the environment. Mining the U. maydis genome identified genes encoding putative CK signalling and biosynthesis proteins.     

小麦散黑穗病空间分布型及抽样技术

本研究拟合出了小麦散黑穗病Ｕｓｔｉｌａｇｏ ｔｒｉｔｉｃｉ（Ｐｅｒｓ．）Ｊｅｎｓ。在麦田的空间分布型属负二项分布，部分也符合奈曼分布（Ａ）型。用Ｉｗａｏ、Ｋｕｎｏ、Ｇｒｅｅｎ和Ｉｗａｏ－Ｋｕｎｏ方法研究，提出了序贯抽样技术、理论抽样数和随机抽样分布点，以供在测报和防治工作中参考。     

玉米黑粉菌cyp51基因上游调控区克隆及生物信息学分析

为探明玉米黑粉菌cyp51基因的表达调控机制,根据玉米黑粉菌cyp51基因cDNA的5'-序列,采用染色体步移技术,获得其5'-上游调控区序列,总长为490bp.利用NNPP分析软件预测转录起始位点,并采用TFSEARCH 1.3软件分析转录因子结合位点.结果显示:转录起始位点位于上游134bp处;上游调控区不仅包含启动子的核心结构序列TATA盒(分别位于-30、-58、-318和-348 bp处)和CAAT盒(分别位于-150、-161和-191 bp处),亦包含多个转录因子结合位点,如AP-4、GATA-1、CdxA、Dfd和Oct-1等;在上游调控序列中嘌呤含量高,而且从-222 bp处开始存在4个连续高嘌呤含量的热激转录因子特异性结合位点(HSE).     

玉米自交系对瘤黑粉病抗性鉴定及遗传多样性分析

为明确30份玉米自交系对瘤黑粉病的抗病性，于2018-2019年在甘肃省定西市安定区凤翔镇进行试验，其中选择高抗品种‘齐319’和高感品种‘掖478’为参照，在玉米 6叶1心期，采用注射法对玉米幼苗接种黑粉菌，在接种的第10天和第20天统计发病率、以第20天的发病率作为鉴定玉米种质抗病性的依据，并对遗传多样性和亲缘关系利用 SSR分子标记进行分析。研究结果表明：接种第10天发病率为3.33%～ 53.33%，第20天发病率为10.00%～86.67%；抗性评价上，表现为抗性的材料有7份，其中抗病的材料有1份，中抗的材料有6份，其余23份表现为感瘤黑粉病；69对多态性SSR引物在32份材料中共扩增出272个等位基因变异，每对引物检测出等位基因数3～6个，平均3.64个，多态性信息量为0.435～0.846，平均 0.764；当遗传相似系数为0.643时，69对SSR引物将32份种质资源分为4组类群，第Ⅰ组有19份材料，其中有8份抗性材料；第Ⅱ组有7份材料，有6份感病材料和1份高感病材料；第Ⅲ组有3份高感病材料；第Ⅳ组有3份高感病材料。抗病材料都集中在第Ⅰ组，其遗传背景较窄。     

茭白“雄茭”和“灰茭”的形成及遗传特性

以浙茭2 号（双季茭）的“雄茭”、“灰茭”和正常茭植株为试材,比较了“雄茭”、“灰茭”
和正常茭植株的株高、叶数、分蘖数、植株地上部（叶片、叶鞘和地上茎）生物量和地上茎的质量、形态
指标,同时研究了杀菌剂、水分、辐照等环境因子对“雄茭”和“灰茭”形成的影响,以及“雄茭”和“灰
茭”的遗传特性。结果表明：“雄茭”植株最高,“灰茭”次之,正常茭最矮;正常茭和“灰茭”分蘖数和
每墩植株地上部鲜质量显著高于“雄茭”;正常茭单个地上茎的鲜质量和体积最大,“灰茭”次之,“雄茭”
最小。田间施用杀菌剂可能是影响“雄茭”形成的主要因素,而辐照、干旱和自然环境条件下“灰茭”均
可形成。“雄茭”和“灰茭”具有遗传稳定性。     

UeRbf1调控菰黑粉菌丝状生长和致病力的作用研究

 基于菰黑粉菌的全基因组序列,克隆得到了UeRbf1(GenBank登录号:MW375682),该基因的开放阅读框为1 281 bp,无内含子,编码426 个氨基酸,经预测具有3个C₂H₂锌指结构域,提示其具有转录调控功能。进一步在菰黑粉菌中敲除UeRbf1后进行体外生长及侵染试验,发现:在体外培养时,UeRbf1的缺失没有改变菌株的生长速率及单倍体形态,也未改变两个性亲和UeRbf1缺失突变体的融合及菌丝形成能力,但是融合菌丝的丝状生长能力显著减弱,而且在侵染时UeRbf1缺失突变体丧失了菌丝形成及丝状生长能力,人工接种野茭后也无法使其茎部膨大。以上结果表明,UeRbf1是调控菰黑粉菌丝状生长和侵染能力的一个重要因子。另外, UeRbf1缺失突变后,在体外融合及侵染时相关丝状生长和致病力的调控因子Biz1、Clp1、Hdp1和UeKpp6呈下调表达,其中Biz1的下调表达最为显著,在突变体中几乎不表达,说明UeRbf1对菰黑粉菌丝状生长和致病力的影响,可能是通过调控Biz1来实现的。     

Smut Disease Incidence and Mineral Composition of Corn as Affected by N Fertilizer Sources and K Application Rates

A 2 year field experiment was initiated to compare the effect of ammonium nitrate (AN) and urea (U) fertilizer sources at 0, 45, 90 and 135 kg N acre⁻¹ in combination with 0 and 48 kg K₂O acre⁻¹ on dry matter yield (DM), smut index (SI) and ear leaf nutrient composition. The plants at 8-leaf growth stage were exposed to artificial infection and the severity was rated on a 1–9 scale. Elemental leaf (N, K, Ca and Mg) and DM were determined at silking and harvest time, respectively. N:(K+Ca+Mg) ratio in plant tissue was calculated. The plants supplied with AN fertilizer appeared to have had greater advantage in DM yield, accompanied by a marked increase in smut severity at higher N rates than U-treated plants. On average, the relative increases in DM and SI for AN were 8.2 and 9.1%, respectively. Potassium application suppressed smut incidence by 19.6%. The leaf analysis data showed that the plants treated with AN were associated with greater cation uptake than LJ-fed plants. Increasing N rates enhancedsmut severity and resulted in remarkable increases in DM and ear leaf nutrient composition. Leaf Ca and Mg contents were decreased hy increasing K3O rates. The correlation coefficients (r) between ear leaf nutrient contents and SI showed variable significant effects among N sources. Because the plant nutrient levels are determined by many variables, attention was drawn to N:(K+Ca+Mg) ratio in plant tissue for better smut disease interpretations.     

Diversity for Disease Resistance in Barley Landraces from Syria and Jordan

A number of barley landraces collected in Syria and Jordan were evaluated for resistance to yellow rust, powdery mildew, scald and covered smut by inoculating single-head progenies with local pathogen strains during two years of field tests. A large diversity in resistance was observed for each pathogen both between populations of different collection sites as well as between head progenies within collection sites. The level of resistance varied from absolute and partial resistant types up to highly susceptible lines. No consistent association between the environmental conditions of the collection site and the level of resistance of the landrace-lines could be found.     

Ustilago kamerunensis on Napier grass in Kenya

Napier or elephant grass, Pennisetum purpureum Schum., is the major source of fodder for stall-fed dairy cattle in Kenya. In the early 1990s, a new disease, caused by Utilago kamerunensis P. & H. Sydow was reported on the grass. Since there was a lack of information on the general pest and disease status of Napier grass in Kenya, a survey was carried out. The survey confirmed that U. kamerunensis was the major pest and disease threat to Napier grass production in the country, having spread to four districts and occurring in 27% of farm plots sampled. The existence of disease hotspots suggests that the main means of spread is through transport of infected planting material, and that the severity of the disease in Kenya compared with other countries results from an increase in the cultivation of Napier grass over the past decade.