Cybrids and tetrad sterility for developing true potato seed hybrids

Potato cybrids result from the fusion between cytoplasm and nuclear gene donors. Such genetic materials are an alternative means to broaden the breeding pool by non‐sexual gene transfer. Tetrad pollen sterility provides also another source of male sterility with some potential for true potato seed breeding. The objective of this research was to investigate cybrid‐derived offspring for both agronomic and reproductive characteristics in two contrasting Peruvian locations, and to examine new exotic germplasm for tetrad sterility, with the aim of broadening the breeding pool available at the Centro Internacional de la Papa (CIP). The cybrids were derived from fusions between Y‐245.7, a clone with tetrad sterility, and Atzimba. These cybrids were crossed with selected male parents from the CIP breeding population, and their hybrid offspring were tested in La Molina (coastal desert) and Huancayo (cool highlands). In addition, other clones with tetrad sterility were also crossed with selected testers to determine their breeding value. There were significant differences for tuber yield, style length, and berry number among the hybrid offspring, and the genotype by environment interaction was significant for tuber yield and berry number. The top 25% highest yielding cybrid‐derived offspring across both locations showed the same tuber yield although they were significantly different for some of the reproductive characteristics. With the exception of one cybrid, the others did not exhibit segregation for tetrad sterility in their hybrid offspring, which were male fertile. However, the offspring derived from crosses between other sources of tetrad sterility and the same testers all showed tetrad sterility, and some of them had outstanding tuber yield at La Molina. The lack of segregation for tetrad sterility in these new crosses suggests that the non‐cybrid, male sterile, female parents are triplex or quadriplex for the Tr nuclear locus, which interacts with a sensitive cytoplasm (e.g. Trs from S. verrucosum or S. stoloniferum) to produce tetrad sterility in potato.     

DETECTION of ENTEROTOXIGENIC CLOSTRIDIUM PERFRINGENS IN GROUND BEEF

Clostridium perfringens is widely distributed in foods. This experiment was performed to assess occurrence of C. perfringens cultures and toxigenic strains isolated from ground beef Samples (118) were collected from 20 locations in Northeast Kansas and the number of C. perfringens was enumerated in these samples by Fung's Double-tube method with tryptose sulfite cycloserine agar medium. Out of 118 samples, 54 (46%) were found positive for C. perfringens. Pure isolates of C. perfringens were further grown in cooked meat medium for 24 h at 42C then heat shocked at 75C for 20 min and inoculated into modified Duncan and Strong medium for production of C. perfringens enterotoxin. Presence of enterotoxin was tested by the reverse passive latex agglutination test (Oxoid), which can detect enterotoxin up to a minimum level of 2 ng/mL. the data indicate that 46% of the beef samples harbored C. perfringens , but only 32 (6%) of 525 isolates were found to produce enterotoxin. This study emphasized the importance of continued surveillance of C. perfringens in meats and meat products and assessment of the toxigenesis of isolates.     

新疆石人沟山区岩面生地衣群落分布格局的环境解释

地衣作为真菌和绿藻/蓝绿藻的成功共生体,广泛分布在陆地生态中的各种栖息地。岩面生地衣作为陆地生态系统的主要组成部分,在干旱和半干旱地区陆地食物链中具有重要地位,同时对岩石的生物腐蚀和土壤的形成有重要作用。岩面生地衣的多样性和分布格局强烈地受到海拔、湿度、温度、降水量、太阳辐射强度和基物的特征(岩石类型、岩石大小、岩石的化学成分和营养成分)等多种因素的影响。为了研究乌鲁木齐县石人沟山区岩面生地衣群落与基物间的关系,该研究在乌鲁木齐县石人沟山区设立16个样地,计测样地中岩面生地衣的盖度,包括坡度、坡向、光照强度等7个环境因子,采用典范对应分析法(CCA)对各群落的物种分布格局与环境因子的关系进行了探讨。结果表明:石人沟山区的岩面生地衣共有27种,隶属于7目9科15属。其中,黄枝衣目、茶渍目和鸡皮衣目的种类较多,占该地区岩面生地衣总数的74.07%。CCA排序结果显示坡度、坡向、光照强度、湿度、岩石pH值是5个影响岩面生地衣种类分布格局的主要环境因子,并显示了岩面生地衣与样地间的对应性。     

RPB2序列的贝叶斯分析估计梅衣科部分谱系分化时间

以树发属(Alectoria)化石为校正点,使用RPB2序列和BEAST分析方法估计梅衣科部分类群的分化时间。梅衣科地衣部分谱系的分化发生在白垩纪、古新世到始新世和渐新世;主要属内辐射则发生在晚始新世、早渐新世,并延续到中新世和上新世早期。估计的主要谱系分化时间与古气候条件及古地质区域分支图相呼应。     

Potato coiled sprout in relation to seed tuber storage treatment and to infection by Verticillium nubilum Pethybr

Inoculation of seed potato tubes with Verticillium nubilum produced infection on the underground stem bases to subsequent growth in the form of brown lesions, often accompanied by longitudinal or transverse cracking. Some inoculation tests provided further evidence of a causal relationship between infection with V. nubilum and coiled sprout, but it was not possible to define the conditions in which the fungus gave rise to coiling. Seed tubers sprouted in light before planting produced more coiling than unsprouted or desprouted tubers. Sprouting had this effect whether V. numbilum was present or not and coiling induced by sprouting and that induced by V. nubilum occurred independently. The increased coiling of stem bases from sprouted tubers was often accompanied by fasciation, whereas this symptom was not usually associated with the coiling from unsprouted or desprouted seed tubers inoculated with the fungus. Brown lesions associated with V. nubilum were readily distinguishable from those of Rhizoctonia solani but not from those caused by Oospora pustulans. Neither of these fungi was found to cause coiling. Different varieties of potatoes showed differences in the incidence of coiling in response to sprouting treatment. There was no apparent differences in varietal response to infection by V. nubilum.     

Marker-assisted selection of high molecular weight glutenin alleles related to bread-making quality in Iranian common wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Bread-making quality in hexaploid wheats is a complex trait. It has been shown that the amount and composition of protein can influence dough rheological properties. The high-molecular-weight (HMW) glutenins are encoded by a complex locus, Glu-1, on the long arm of group-1 homoeologus chromosome of the A, B and D genomes. In this work we used PCR-based DNA markers as a substitution tool to distinguish wheat bread-making quality. We detected PCR-based DNA markers for coding sequence of Glu-A1x, Glu-B1x and Glu-D1x to be 2300 bp, 2400 bp and 2500 bp respectively. DNA markers related to coding sequence of Glu-A1y, Glu-B1y and Glu-D1y were; 1800 bp, 2100 bp and 1950 bp, however, the repetitive region of their coding sequence were shown to be about 1300 bp, 1500 bp and 1600 bp. The results demonstrate that the size variation was due to different lengths of the central repetitive domain. Good or poor bread-making quality in wheat is associated with two allelic pairs of Glu-D1, designated 1Dx5-1Dy10 and 1Dx2-1Dy12. The 1Bx7 allele has moderate-to-good quality score. The specific DNA markers, of 450 bp, 576 bp, 612 bp and 2400 bp respectively were characterized for 1Dx5, 1Dy10, 1Dy12 and 1Bx7 alleles. These markers are very important in screening of wheat for bread-making quality.     

Variation in cardinal temperatures for germination among wheat (Triticum aestivum) genotypes

In most tropical regions where wheat is grown under irrigation, high temperatures at sowing adversely affect crop establishment and subsequent seedling survival. The objective of this study was to compare wheat (Triticum aestivum) genotypes for their ability to germinate and grow at high temperatures during the seedling stage. Twenty-five seeds each of 14 spring wheat cultivars were placed on moist filter paper at different temperatures (5°C to 40°C) in a one-way thermogradient plate to determine the cardinal temperatures for germination. Rate of germination at each temperature for each genotype was computed as the inverse of time taken for 50% of the seeds to germinate. Rate of germination for each genotype at different temperatures was modelled with temperature to determine the base (t_b), and optimum (t_opt) temperatures. Response of germination to temperature for each genotype was calculated as the slope of a linear regression of the rate of germination on temperature below t_opt. Genotypes differed in their optimum temperatures and Mexipak (= Kalyansona) had the lowest. Range in base temperature among the genotypes was between 0°C and 2°C differences but were not statistically significant though they might be biologically significant. Genotypes differed in their response to temperature with Gomam having the lowest rate, implying that it was slow to respond to increasing temperatures. Debeira and Cham 6 showed a similar response. Three lines which had performed well in spring wheat evaluation trials for moderate rainfall areas under heat stress had the highest response rate. It is concluded that combining higher optimum temperatures with faster response rates would result in better-adapted germplasm for regions where high temperatures persist at sowing.