Ear rot,aflatoxin accumulation,and fungal biomass in maize after inoculation with Aspergillus flavus

Aflatoxin, a toxin produced by the fungus Aspergillus flavus Link: Fries, occurs naturally in maize (Zea mays L.). Aflatoxin is a potent human carcinogen and is also toxic to livestock, pets, and wildlife. When contaminated with aflatoxin, the value of maize grain is markedly reduced. This investigation was conducted to compare ear rot, aflatoxin accumulation, and fungal biomass in maize single crosses with varying degrees of resistance to aflatoxin accumulation and to determine the relative importance of general combining ability (GCA) and specific combining ability (SCA) in the inheritance of resistance to ear rot, aflatoxin accumulation, and fungal biomass. Eight germplasm lines with different levels of resistance to aflatoxin accumulation were used as parents of a diallel cross. The cross was evaluated for visible ear rot, aflatoxin accumulation, and A. flavus infection in the grain. A. flavus infection was determined by quantitative real-time polymerase chain reaction (qRT-PCR) assays. Both GCA and SCA were significant sources of variation in the inheritance of the three traits although GCA accounted for a greater portion of the variation among single crosses. The interactions of GCA and SCA with years were highly significant for aflatoxin accumulation, but not significant for A. flavus infection. Estimates of GCA effects were highly significant for both reduced A. flavus infection and reduced aflatoxin accumulation for Mp313E, Mp715, and Mp717. Conversely, GCA effects associated with GA209 were significant for reduced levels of A. flavus infection and ear rot, but high levels of aflatoxin accumulation. Mp313E, Mp715, and Mp717 should be useful in breeding programs targeting both reduced levels of fungal infection and aflatoxin accumulation.     

Diallel analysis for aflatoxin accumulation and fall armyworm leaf-feeding damage in maize

Two major impediments to profitable maize, Zea mays L., production in the southern United States are from feeding by fall armyworm, Spodoptera frugiperda (J.E. Smith), and losses from the production and accumulation of aflatoxin in maize grain. A diallel cross was produced by making all possible crosses among five germplasm lines developed as sources of resistance to fall armyworm leaf feeding and five lines developed as sources of resistance to aflatoxin accumulation. For resistance to both leaf feeding and aflatoxin accumulation, general combining ability (GCA) was a significant source of variation. Specific combining ability (SCA) was significant for fall armyworm feeding only. Estimates of GCA effects for reduced aflatoxin accumulation were significant for Mp715 and Mp719, two lines selected for resistance to aflatoxin accumulation. The GCA effects for reduced fall armyworm damage were significant for all five lines selected for fall armyworm resistance: Mp707, Mp708, Mp713, Mp714, and Mp716.     

Diallel analysis of aflatoxin accumulation in maize

Since its discovery in numerous feedstuffs, aflatoxin, a carcinogenic compound produced by the fungus Aspergillus flavus Link ex Fries, has caused much concern among consumers and producers alike. This toxin poses a serious economic threat to maize (Zea mays L.) producers of the southeastern and midwestern regions of the United States. Efforts to identify maize germplasm that is resistant to aflatoxin accumulation and to investigate the genetic basis of this resistance have been undertaken at numerous research institutions. The objectives of this study were to (1) evaluate aflatoxin accumulation in grain harvested from maize inbred lines and a diallel cross among these lines, (2) determine the importance of general and specific combining abilities in inheritance of resistance to aflatoxin accumulation, and (3) estimate general and specific combining ability effects associated with resistance to aflatoxin accumulation in the inbred lines and crosses among them. Eight inbred lines and a diallel cross of the maize lines were inoculated with an A. flavus spore suspension 12–14 d after silk emergence. Following harvest, aflatoxin content was determined from samples of grain. Statistical analyses performed using SAS general linear models (GLM) and DIALLEL-SAS indicated that general and specific combining ability were significant sources of variation in the inheritance of resistance to aflatoxin accumulation. The inbred line Mp313E, which was developed and released as a source of resistance to aflatoxin contamination, had significantly lower aflatoxin accumulation than other lines. Mo18W exhibited excellent general combining ability for reduced aflatoxin accumulation when crossed with the other lines. Both Mp313E and Mo18W could be useful in breeding programs to develop aflatoxin-resistant maize hybrids. Mp339, SC212M, and Ab24E demonstrated aflatoxin susceptibility as both inbreds and in single crosses.     

Combining ability analysis for Phaeosphaeria leaf spot resistance and grain yield in tropical advanced maize inbred lines

Phaeosphaeria leaf spot (PLS) disease (causal agent Phaeosphaeria maydis (Henn.) Rane, Payak & Renfro) of maize is increasing in importance in sub-Saharan Africa (SSA). However, there is still limited information on the combining ability for disease resistance of the germplasm that are adapted to African environments. Evaluating combining ability effects and their interactions with the environment would provide valuable information that can be used in the development of cultivars that are resistant to PLS. This study was therefore conducted to determine the combining ability, gene action and the relationship between grain yield and PLS disease severity among selected tropical advanced maize inbred lines. Forty five F₁ hybrids were generated by crossing 10 inbred lines in a half diallel mating scheme. The 45 hybrids along with the ten inbred parents were evaluated in four environments, with two replications each between 2007 and 2009. General and specific combining ability (GCA and SCA) effects were highly significant (P ≤ 0.001) for PLS, grain yield and days to anthesis. GCA effects accounted for 66–90% and SCA effects for 10–34% of the variation in the hybrids for PLS resistance, grain yield and days to anthesis. This indicated predominance of additive over non-additive gene action for the three traits in these inbred lines. The resistant inbred lines to PLS were A1220-4, N3-2-3-3, CML312, MP18 and CML488. These lines had good combining ability for PLS resistance and contributed towards resistance in their crosses. In general, resistant hybrids involved a susceptible and a resistant parent, where at least one of the parents had a negative GCA effect. In addition, lines A1220-4 and CML312 contributed towards high yield and were late maturing. Inbred line CZL00009 conferred genes for early maturity. Linear regression analysis indicated that grain yield of maize was suppressed by about 250 kg ha⁻¹ per each increase in PLS disease severity score, underscoring the need to control the disease. Significant (P < 0.01), negative correlations (r = −0.29 to −0.43) between grain yield and PLS severity were also detected. This showed the potential of PLS to reduce yield when favourable conditions for disease development are present. By and large, highly significant additive gene action implied that progress would be made through selection. Although non-additive effects were small (±10%), observation of dominance effects which were associated with reduced disease levels in some hybrids may be exploited in developing single cross maize hybrids among these inbreds when one parent is resistant.     

Genetic analysis of early-maturing maize (Zea Mays L.) inbred lines under stress and nonstress conditions

Early-maturing maize (Zea Mays L.) germplasm developed from diverse sources has the potential for use in developing maize hybrids suitable for increasing maize production in the dry ecologies of eastern Africa. A diallel study was conducted to estimate general combining ability (GCA) of 12 early-maturing maize inbred lines, identify potential single-cross hybrids for use as parents, assess genetic diversity among the inbred lines, and relate genetic distance to specific combining ability (SCA) and hybrid performance. Sixty-six F₁ diallel hybrids were evaluated under optimal and drought stress conditions at four locations in Kenya and Uganda. The parental inbred lines were genotyped using 94 single nucleotide polymorphism (SNP) markers. Additive gene action was more important than nonadditive gene action for inheritance of grain yield (GY) under optimal conditions. However, nonadditive gene effects were more important in the inheritance of GY under drought and across all environments. Inbred lines CKL0722, VL058014, and CZL0724 were among the best with positive GCA effects for GY across both optimal and drought stress conditions. The correlation between SCA and both genetic distance and F₁ GY was significant under both drought stress and across all environments. Inbred lines with desirable GCA effects for GY and other agronomic traits and hybrids with good performance under both optimal and drought stress conditions are potential parents for development of various types of high-yielding, stress-tolerant, and early-maturing hybrids.     

Lancaster群体改良自交系株型性状的配合力分析

采用不完全双列杂交,分析8个含有Lancaster血缘的自交系与4大类群代表系中5个自交系的一般配合力(GCA)和特殊配合力(SCA)。结果表明：株高、穗位高、茎直径、雄穗长、雄穗分枝的GCA和SCA方差均达极显著水平;一般配合力及小区产量较高的自交系有N305、N575、N583、吉853、丹340、丹988;N575×丹340的总配合力效应值最高,是最好的杂交组合。在供试的8个自交系中,N575、N583、N305与各父本所配杂交组合产量较高,是比较理想的自交系。株型性状间的相关分析表明,株高与穗位高、雄穗长度有较大的正相关,穗位高与茎直径相关性较大。     

1O个玉米自交系主要性状的配合力研究

试验采用5×5不完全双列杂交设计,对10个玉米自交系的一般配合力和特殊配合力进行了分析。结果表明：在利用一般配合力较高的自交系作为杂交亲本时,兼顾特殊配合力可以组配出更强优势的杂交组合。     

Protein quality and endosperm modification of quality protein maize (Zea mays L.) under two contrasting soil nitrogen environments

Quality protein maize (QPM) breeding involves the combined use of the opaque-2 (o2) gene and the genetic modifiers of the o2 locus to develop cultivars with modified kernel endosperm, and increased concentrations of lysine and tryptophan. This study was designed to assess grain yield performance, endosperm modification, and protein quality and quantity under two contrasting soil nitrogen environments. A 15-parent diallel cross was evaluated under one low nitrogen stress and one optimal nitrogen environment each at Harare (Zimbabwe) and Bako (Ethiopia). Most QPM hybrids showed higher protein quality levels than the best non-QPM check under both conditions. Protein concentration tended to vary across nitrogen levels, but not endosperm type. Significant differences were found for the test of main effect (nitrogen-level) for endosperm modification and tryptophan concentration. This indicated that QPM maintains quality even under low soil nitrogen, a widespread condition in Africa. General combining ability (GCA) mean squares were highly significant for most protein quality traits for each environment and across environments whereas specific combining ability (SCA) mean squares were not significant in most cases. This indicated that additive gene effects were primarily responsible for variation of most traits evaluated and hence progeny performance can adequately be predicted on the basis of parental performance. Inbred lines P2, P4 and P12 had desirable GCA effects for endosperm modification while P1 and P3 had the best GCA for tryptophan concentration in grain. The current study suggests that hybrids with desirable endosperm modification, protein quality and stable performance under low nitrogen stress and optimal conditions can be produced with careful selection.     

"金皇后"等八个玉米群体产量配合力分析

通过8个玉米群体双列杂交分析,研究其产量配合力及杂种优势.产量方差分析结果表明,基因型之间差异极显著.产量的一般配合力和特殊配合力差异均极显著.群体豫综5号、黄墨49、金皇后、二南24群和自T36具有较高的一般配合力和较大的特殊配合力方差.群体黄墨49产量的一般配合力效应值最高.金皇后的一般配合力效应值在8个群体中处于中等水平.BSSS和Lancaster群的一般配合力效应值偏低.金皇后×黄墨49产量最高.BSSS×自T36中亲优势最高.根据群体产量的配合力和杂种优势分析,初步筛选出豫综5号×自T36、豫综5号×二南24、金皇后×黄墨49和金皇后×自T36四个潜在的杂优组合模式。     

优良玉米自交系苏951的配合力分析及应用

苏951是江苏省农业科学院粮食作物所选育的优良玉米自交系,利用苏951已经育成一批优良组合。根据玉米杂种优势群和杂种优势模式,按不完全双列杂交模式组配了20个杂交组合,对苏951的一般配合力和特殊配合力进行分析评价苏951的育种特性。研究结果表明：除穗行数外,苏951的大部分产量性状的一般配合力较高,与塘四平头群、PN群有较强的杂种优势。     

Inheritance of resistance toFusarium sulphureum in crosses betweenS. tuberosum potato cultivars measured on field and glasshouse grown tubers

Summary Solanum tuberosum potato cultivars with differing levels of resistance to dry rot caused byFusarium sulphureum were hybridised in a half diallel crossing programme. Glasshouse grown tubers from true seedlings and field-grown tubers of the resulting progenies were assessed for their resistance toF. sulphureum. Statistical analysis revealed differences between the progenies forF. sulphureum resistance on both field and glasshouse grown tubers. On the field grown tubers, differences between progenies were due to differences in the general combining ability (GCA) of the parents. Parental phenotypes and GCA values were highly correlated. Overall. GCA was consistent for resistance or susceptibility, and glasshouse grown progenies showed a good correlation for GCA between years (r=0.85^***), and with the results of the field grown progenies (r=0.61^* in 1998 and r=0.69^** in 1999). It appears that resistance toF. sulphureum is heritable, and that this heritability is better assessed on field grown rather than glasshouse grown tubers, although the two are largely in agreement.     

Estimation of combining ability for yield and yield components in rice (Oryza sativa L.) cultivars using diallel cross

In order to estimate combining ability and gene action of a number of rice cultivars, a 5 x 5 half a diallel cross genetic design has been used. Parents and their hybrids have been evaluated in a randomized complete block design with 3 replicates for yield and 6 yield components in 2007 in Rice Research Station of Iran-Amol. Mean squares of genotypes for all traits were highly significant (p < 0.01). Significant mean squares of combining ability for all traits showed additive and non-additive effects in control of the related traits. Having nonsignificant MS(GCA)/MS(SCA) ratio for all traits but 1000-grain weight show higher importance of nonadditive effects in comparison with additive effects of controlling genes. High relative importance of specific combining ability indicated that all traits but 1000-grain weight are highly affected by impacts of specific combining ability. Generally, Dasht, Neda and Binam were the best parents for general combining ability and Binam x IR62871-175-1-10 and Mashhad Domsiah x Binam were the best hybrids for grain yield and its components.     

12个粳稻新不育系的配合力及利用价值评价

以12个新育成的BT型粳稻不育系和8个恢复系为亲本,采用p×q不完全双列杂交(NCⅡ)设计,对其F1代13个农艺性状的配合力进行了分析。除单株穗数的特殊配合力方差不显著外,所有性状的一般配合力方差和特殊配合力方差均达到极显著水平。所测性状主要受亲本一般配合力的影响,主穗实粒数、结实率、单株产量和收获指数受组合特殊配合力的作用较突出。穗长、穗颈长、结实率和收获指数受不育系的影响较大,其余性状均受恢复系的影响较大。亲本一般配合力和组合特殊配合力是相互独立的。一般配合力和特殊配合力与杂种优势呈极显著正相关。不育系以六盐A、丹阳941A、98G26A、99 9A、香粳8016A和95122A较好,有较大的应用潜力;恢复系以C418、J16、晚161和C76较好。     

19个玉米自交系主要数量性状配合力分析

以19个贵州地方玉米自交系为亲本,按不完全双列杂交(9×10)配成90个杂交组合,对株高、穗位、穗粒重等10个主要性状进行了方差分析,并在此基础上进行了配合力分析。结果表明,在一般配合力相对效应值上,各亲本的不同性状的效应值不同,选出了1、12、14、17等4个比较优良的自交系;在特殊配合力相对效应值上,所有组合不同性状的各个效应值的排名不同,其中12、34、26等是比较优良的杂交组合。总配合力分析得出,穗粒重总配合力相对效应值的前10位的组合分别为68、3、35、33、85、81、38、53、9、8。     

玉米籽粒几个物理性状的遗传与配合力分析

用14份玉米自交系采用7×7不完全双列杂交设计组配的49个F1组合为供试材料,研究了玉米籽粒几个物理性状的遗传规律和配合力效应。结果表明,粒宽和容重主要受加性基因效应影响;千粒重和比重加性效应及非加性效应同等重要;粒长主要受非加性效应影响。同一物理性状在不同自交系间其GCA效应有较大差异,其中自交系5003的粒长GCA效应最高,533粒宽和比重GCA效应均为最高,千粒重和客重GCA效应最高者分别为425和48—2。     

玉米花粉诱导小黑麦单倍体的诱导率遗传规律分析

为揭示玉米花粉诱导小黑麦产生单倍体中诱导率的遗传规律,以六个诱导率不同的春性小黑麦品系为材料,采用完全双列杂交方法,对与小黑麦单倍体诱导率相关的颖果率、得胚率、颖果得胚率及成苗率的配合力、遗传力及杂种优势等进行了分析。结果表明,小黑麦亲本的颖果率、颖果得胚率、得胚率及成苗率一般配合力(GCA)差异较大,品系08春H区61和08春H鉴25颖果率的GCA效应值较高,而品系08春H鉴10得胚率的GCA效应值最高。四个性状的特殊配合力(SCA)效应值也有较大差异,同一性状在不同组合间SCA效应值的变幅也较大,颖果率的SCA效应值变幅为-14.23~36.21,得胚率的SCA效应值变幅为-20.32~25.65,颖黑得胚率的SCA效应值变幅为-9.58~18.11,成苗率的SCA效应值变幅为-0.99~5.31。四个性状的母体遗传效应所占遗传分量均最大,非遗传效应次之。得胚率、颖果得胚率和成苗率的超亲优势均达到了极显著水平,且均表现为负向优势,颖果率的超亲优势和中亲优势在参试杂交组合中的变幅最大。四个性状的狭义遗传力均超过40%,其中成苗率的狭义遗传力最高(67%);得胚率、颖果得胚率以及成苗率的广义遗传力分别为41.46%、59.52%和66.80%,都达到了极显著水平。可见,根据母本的诱导率,参考配合力高低选择优良F1代进行诱导有利于提高玉米花粉诱导小黑麦单倍体的效率。     

十个玉米自交系主要数量性状配合力和遗传参数分析

利用10份玉米自交系按不完全双列杂交配成25个组合,对其主要数量性状的GCA、SCA和遗传变量进行估算和分析.结果表明,除穗位高、千粒重、出籽率和子粒产量的SCA外,其余各性状的GCA和SCA都达到显著或极显著差异.H504、同系和82-2A等3个自交系综合性状较优,可组配强优势杂交组合的优良自交系。     

杂交稻淀粉RVA谱特征值的配合力及杂种优势研究

以6个籼型三系杂交稻不育系和5个恢复系按不完全双列杂交配制的30个杂交稻组合及其亲本为材料,对其淀粉RVA谱特征值进行了测定和分析。结果表明:淀粉RVA谱特征值在各组合间均存在极显著遗传差异,其加性效应和非加性效应对杂交稻淀粉RVA谱特征值均存在极显著的影响,并以加性效应为主;杂交稻亲本RVA谱特征值一般配合力(GCA)效应高的,其后代特殊配合力(SCA)效应不一定高;杂交稻母本RVA谱特征值GCA方差在总的基因型方差中所占比重远远大于父本和组合SCA方差,表明杂交稻淀粉RVA谱特征值主要受不育系的影响;杂交稻淀粉RVA谱特征值的竞争优势与母本的GCA极显著正相关,且决定系数较高,表明杂交稻母本的一般配合力高,其所配杂交稻组合的竞争优势也强;杂交稻淀粉RVA谱特征值的峰值黏度存在明显的超高亲优势;糊化开始温度存在超低亲优势;其他性状存在中亲优势。     

玉米自交系08-641不同选择方向回交改良后代主要性状的配合力

利用不完全双列杂交设计对玉米自交系08-641(R08)不同选择方向回交改良后代主要性状的配合力进行分析。结果表明,两种选择方向的回交后代均能在相当程度上保持轮回亲本R08的一般配合力(GCA),以种子形状和颜色不似R08为标准选择得到的回交后代株系GCA有所提高的性状相对略多于以种子形状和颜色似R08为标准选择得到的回交后代株系,部分回交后代部分性状GCA显著降低。改良系BCML50主要性状一般配合力高,且与测验种RP125有较高的特殊配合力,是优良的改良系。     

Heritability of resistance in maize to sorghum downy mildew (Peronosclerospora sorghi (Weston and Uppal) C.G. Shaw)

Host-plant resistance is an effective and economical means of controlling downy mildew (DM) diseases in maize (Zea mays L.). Crosses involving 10 inbred maize lines in all possible combinations (diallel cross) showed that susceptibility to sorghum DM (Peronosclerospora sorghi (Weston and Uppal) C. G. Shaw) is generally inherited as a dominant characteristic. However, progenies of crosses between one of the lines (CM105) resistant to DM, and susceptible lines, showed intermediate levels of resistance, indicating that several genes are involved and that their effects are additive. Progenies of crosses between resistant lines were more resistant than their parents, probably because of interactions between different resistance genes (epistasis). Both additive and non-additive gene action was detected by partitioning gene effects by generation mean in each 16 DM-resistant × DM-susceptible combinations, which indicates that the reactions of maize to DM are governed by several genes (i.e. polygenically) and that the inheritance of resistance is complex. An inbred line from Mexico, Tuxpeno Gpo. 48-Var. 168-1, is a particularly promising general source of resistance to DM.