Additive inheritance of resistance to pod rot caused by Phytophthora palmivora in cocoa

Summary Quantitative inheritance of resistance to Phytophthora pod rot (Ppr) was studied in cocoa hybrid progeny from 12 Trinitario x Amazonian crosses and their reciprocal crosses. The crossing scheme was similar to a factorial design. Disease was assessed by the number and percentage of infected pods on each tree. Highly significant differences due to general combining abilities (GCA) were obtained for all characters, except for the GCA of Trinitario on total pod production. Differences for specific combining ability (SCA) were not significant for all characters. There were no significant differences between reciprocal crosses. The Trinitario clone K82 provided the only source for the hybrid progenies of strong Ppr resistance to the hybrid progenies, while K20 provided moderate resistance. Other parental clones — KA2-101, KA5-201, KEE 2, KEE 5, and KEE 52 — produced progenies which were susceptible to Ppr. It is evident that resistance to Ppr in cocoa is inherited additively. Maternal and cytoplasmic effects were assumed to have no influence on inheritance of resistance. It is also concluded that resistance to Ppr of the kind shown by K82 is likely to be horizontal resistance. Breeding for high-yielding cultivars combined with Ppr resistance is the most effective way of controlling Ppr of cocoa on the crops of growers with small holdings in Papua New Guinea.     

Producing commercially attractive,uniform true potato seed progenies: the influence of breeding scheme and parental genotype

The production of attractive, uniform true potato seed (TPS) progenies was investigated. Four breeding schemes were compared: intercrossing tetraploid cultivars (cv x cv); doubled dihaploids x cultivars (ddh x cv); cultivars x diploid unreduced-gamete producers (cv x FDR) and doubled dihaploids x diploid unreduced-gamete producers (ddh x FDR). Fifty three progenies and five clones were grown in a glasshouse in a randomised complete block design with three replicates of 25 plants per progeny and clone. Each plant's tubers were counted and the colour, shape, quality of skin finish, flesh colour, and commencai attractiveness (which includes yield) recorded. The most uniform progenies were also selected by visual comparison with the clones. For mean attractiveness, differences (P < 0.001) between breeding schemes and between progenies within breeding schemes were detected. The cv x cv and cv x FDR progenies were more attractive than clonal controls. There were significant additive and non-additive effects for attractiveness in all breeding schemes except cv x FDR. There were between-progeny differences (P < 0.001) for uniformity for all characters. Progenies uniform for one character could be variable for other traits. Breeding schemes gave different levels of uniformity (P < 0.001) for all characters except shape and flesh colour, but none gave low levels of variation for all traits. Doubled-dihaploid parents increased the variation in progenies. There were uniformity differences (P < 0.001) between progenies within breeding schemes for all characters. Evidence of additive and nonadditive genetic variation for uniformity in all traits was detected. In each breeding scheme, parents with good general combining ability (GCA) for uniformity in several characters were identified. Visually selected uniform progenies had parents with good GCAs for uniformity in a range of traits and high specific combining abilities (SCAs) for several traits. A desynaptic first-division restitution (FDR) clone and a male-sterile doubled-dihaploid clone had the best GCAs for tuber uniformity in TPS progenies. Achieving multitrait uniformity in TPS is problematic but may be aided by the selection of parents with GCAs for uniformity coupled with progeny testing to allow for non-additive effects.     

Combining ability for resistance in peanut (Arachis hypogaea) to Peanut bud necrosis tospovirus (PBNV)

The combining abilities of field resistance to peanut bud necrosis disease (PBND) caused by Peanut bud necrosis tospovirus (PBNV) were examined to understand the type of gene action governing resistance to the disease, and to identify peanut lines suitable for use as parents in a PBND‐resistance breeding programme. The Ft and F2 progenies from a six‐parent diallel cross and their parents were evaluated under field conditions. They were assessed for disease incidence at 30, 40, 50 and 60 days after planting (DAP), and reactions of the lines to the disease could be best differentiated at 50 and 60 DAP. Results indicated highly significant general combining ability (GCA) effects for PBND incidence in F₁ and F₂ generations. Specific combining ability (SCA) and reciprocal effects were also found to be significant, but their relative contributions to variation among crosses were much less than those of GCA effects. These results suggested that the type of gene action governing resistance to PBND was mainly additive, and selection for PBND resistance in these populations should be effective. Strong correlation coefficients between parental means and GCA effects for disease incidence were seen in both Ft and F2 generations, suggesting that per se performance of the parental line could be used as a predictor of the capability of the line to transmit its PBND‐resistant attribute to progenies. The reciprocal effects were in favour of using resistant lines as female parents. The peanut lines ICGV 86388, 1C 10 and 1C 34 were found to be suitable for use in a PBND–resistance breeding programme.     

小麦品质和农艺性状的配合力分析

依据田间试验和室内生化分析数据,按ｐｘｑ交配模式,对１０个冬小麦亲本２５个杂交组合Ｆ１的蛋白质含量,赖氨酸含量,穗粒重和千粒重的一般配合力和特殊配合力效应进行了分析。结果表明,除蛋白质含量的ｓｃａ外,其余性状的ｇｃａ和ｓｃａ效应均达极显著水平,表明在本研究中,基因的加性效应和非加性效应均起重要作用。由于一般配合力差δ＾２ｓｃａ大,表明基因的加性效应更加重要。根据ｇｃａ,ｓｃａ和δ＾２ｓｃａ估值,分     

甘蓝型油菜对菌核病抗耐病性的育种潜力研究

用细胞质雄性不育系陕 2 A、波里马 A(Pol A)、1 763A与 92 P187、垦 C1、垦 C8、L4 54个恢复系进行不完全双列杂交 ,以其 F1代为试验材料 ,在菌核病田间自然萌发和人工接种菌核病菌的条件下 ,调查了各组合的发病率和病情指数 ,估算了亲本及其组合抗 (耐 )菌核病的配合力效应。结果表明 :1 1 2个杂交种抗 (耐 )病性差异较大 ,以陕 2 A为母本的组合表现出较强的抗 (耐 )病性。 2油菜抗 (耐 )菌核病遗传是由基因的加性效应和非加性效应共同控制的 ;杂种抗 (耐 )病性的变异 ,遗传的作用是主要的 ,而在遗传作用中显性作用又是主要的。 3陕 2 A病情指数的遗传负效应值较高 ,具有作为抗源亲本的育种潜力。 4根据配合力总效应值评价组合 ,认为陕 2 A×垦 C8、陕 2 A×垦 C1、1 763A×垦 C8、陕 2 A× L4 5、Pol A×垦 C1、Pol A× 92P187是抗 (耐 )菌核病较强的杂交组合     

Inheritance of the external mechanical damage resistance of potato cultivars

The examination of nine potato cultivars for external mechanical damage resistance found that tests involving the damage index of Robertson (1970) were reasonably consistent over five years. Progeny testing of eight cultivars in two years, by means of a half diallel with selfs, showed that all of the progeny variation was due to general combining ability and there was no evidence of significant specific combining ability. Ranking of cultivars by damage index was significantly correlated with their ranking by general combining ability from their progenies. The results indicate that the best parents for breeding to improve damage resistance can be predicted using their own damage index.     

对生玉米产量性状的杂种优势和配合力分析

本文利用对生基因转育获得的对生与互生自交系及其杂交组合,研究了对生性状对产量性状杂种优势和配合力的遗传效应的影响。结果表明:对生玉米同互生玉米一样具有普遍的杂种优势,在产量性状上F1对生株优势互×互组合大于对×对组合和对×互(互×对)组合;对生性状的转育对产量性状的一般配合力有降低效应,而含有对生基因的互生玉米具有较高的一般配合力效应,因此,在对生玉米育种中可以利用含有不同对生基因的互生自交系作亲本来组配杂交组合(互×互),从而获得较高的制种产量和高产的对生杂交种。     

Genetic analysis of panicle and physiological traits in hill rice grown in mid altitudes of northeastern India

This paper aims to discover the genetic parameters underlying the physiological efficiency and panicle characters of hill rice plants. In order to improve these characters, it is crucial to learn the nature and magnitude of gene action involved in inheritance of panicle and physiological traits. With this purpose, we combined a line × tester analysis of crosses involving local cultivars and indigenous and exotic germplasm grown at the northeastern hill region of India. From the study it follows that number of tillers per hill, number of ear bearing tillers per hill, panicle length, panicle weight, number of grains per panicle, number of filled grains per panicle, pollen fertility, spikelet fertility, leaf area index, total chlorophyll content and harvest index were mainly under the control of non-additive gene action, while total dry matter accumulation and grain yield per plant were under the control of additive gene action. The genotypes DR 92, Ngoba, IET 16451 and UPR 1425-1-1-4 were identified as superior parents with high performance and significant general combining ability effects. For heterosis breeding six cross combinations, viz., DR 92/IET 16471, DR 92/UPR 1425-1-1-4, DR 92/IET 15482, Ngoba/IET 16469, Ngoba/H274-27-24, Manipuri/IET 16451, and for recombination breeding two cross combinations, viz., DR 92/IET 16470 and Ngoba/UPR 1425- 1-1-4, were found suitable to ameliorate the panicle and physiological traits of hill rice grown in northeastern India.     

Combining ability analyses of stability parameters and forage yield in smooth bromegrass

Summary Twenty-one progenies of smooth bromegrass (Bromus inermis Leyss.) from a 7 X 7 half diallel cross, with their parents, were evaluated for three years at four locations in Alberta for the genetic variation of stability in expression of their annual yield. The linear response and deviation from linear response for each genotype were the two stability parameters considered, together with mean performance in the evaluation of each genotype. Four high yielding genotypes, namely 12, 13, 16, and 26, had general adaptability, while genotype 23 was especially suited to a poor environment. Combining ability analysis showed that general combining ability (GCA) and specific combining ability (SCA) were both important in the expression of yield. Inheritance of linear regression was controlled predominantly by GCA whereas both GCA and SCA were equally important in the expression of deviation. The presence of a substantial proportion of variability due to the additive genetic component in the linear response suggests that it should be possible to exploit this fraction of variability in developing high yielding stable cultivars.     

小麦品种间杂种优势与配合力分析

对９个冬小麦亲本１３个性状的杂种优势分析表明,产量性状的杂种优势较强,品质性状的杂种优势较弱。籽粒蛋白质含量、硬度和湿面筋、干面筋含量偏低亲或中亲遗传,沉淀值偏高遗传,存在较明显杂种优势（１６．１－２３．８％）。     

Combining ability analysis over F1-F5 generations in diallel crosses of bread wheat

Summary Combining ability studies for grain yield and its primary component traits in diallel crosses involving seven diverse wheat cultivars of bread wheat (Triticum aestivum L.) over generations F₁-F₅ are reported. The general and specific combining ability variances were significant in all generations for all the traits except specific combining ability variance for number of spikes per plant in the F₅. The ratio of general to specific combining ability variances was significant for all the traits except grain yield in all the generations. This indicated an equal role of additive and non-additive gene effects in the inheritance of grain yield, and the predominance of the former for its component traits. The presence of significant specific combining ability variances in even the advanced generations may be the result of an additive x additive type of epistasis or evolutionary divergence among progenies in the same parental array. The relative breeding values of the parental varieties, as indicated by their general combining ability effects, did not vary much over the generations. The cheap and reliable procedure observed for making the choice of parents, selecting hybrids and predicting advanced generation (F₅) bulk hybrid performance was the determination of breeding values of the parents on the relative performance of their F₂ progeny bulks.     

Genetic aspects of resistance to cocoa swollen-shoot virus in Ghana

The inheritance of resistance in cocoa to infection with cocoa swollen-shoot virus was studied in seed inoculation experiments with progenies of Upper Amazon, Trinitario and West African Amelonado parents. In an eight parent diallel cross grown in two seasons and in six male × female factorial experiments, general combining abilities were much more important than specific combining abilities. The diallel cross revealed significant maternal effects but there was little evidence of specific reciprocal differences. Estimates of general combining abilities corresponded with expectation and were positively correlated with maternal effects, the latter indicating that tester parents should be used as males. The results from scaling tests with hybrids between selections from the River Nanay (a Peruvian tributary of the River Amazon) and Amelonado fitted a model with additive resistance; there was no evidence of dominance. Attempts to obtain stronger sources of resistance by hybridisation and selection were unsuccessful. In three crosses the resistance of individual seedlings was compared with that of the parents using test crosses but no evidence of transgressive segregation was obtained. In further experiments seedings of two hybrids between contrasting parents were heavily inoculated with virus so that few healthy survivors remained. Test crosses showed that these survivors and randomly selected seedlings of the same parentage did not differ as resistance sources.     

Selection for increased nodule number in common bean (Phaseolus vulgaris L.)

Common bean (Phaseolus vulgaris L.) plants were grown for 21–28 days in plastic container-modified Leonard jar assemblies and placed in a controlled-environment room. The nodules on each plant were removed, counted; selected plants were repotted, grown and intercrossed to produce progenies for the next cycle of recurrent selection. Among the ten parent lines, Puebla 152 and WBR 22–34 produced the most nodules and Rio Tibagi and Negro Argel the fewest, when averaged over five experiments. An analysis of number of nodules on F₁ plants resulting from crosses made in a partial diallel design among the ten parents revealed highly significants variation for general combining ability (GCA) but not for specific combining ability (SCA). After three cycles of recurrent selection for nodule number per plant, the mean nodule number was 211% of the mean for the 10 parents control. Total nodule weight on selected plants also increased, but individual nodule weight decreased. Nineteen C₁ and 18 C₂ lines resulting from the individual plants selected for greater nodule number, along with the ten parents and two non-nodulating soybean lines included as non-fixing check plants were grown in a single experiment in a low-N field. C₂ lines on average accumulated significantly more N per plant than either the parents or C₁ lines, providing evidence for increased N₂ fixation measured by the N difference method. These data show that more nodules, possibly resulting from greater susceptibility to nodulation, are an important, heritable component of symbiosis and that selection for increased nodule number resulted in lines capable of fixing more atmospheric N₂.     

Cassava breeding: opportunities and challenges

Although cassava is a major food crop, its scientific breeding began only recently compared with other crops. Significant progress has been achieved, particularly in Asia where cassava is used mainly for industrial processes and no major biotic constraints affect its productivity. Cassava breeding faces several limitations that need to be addressed. The heterozygous nature of the crop and parental lines used to generate new segregating progenies makes it difficult to identify parents with good breeding values. Breeding so far has been mainly based on a mass phenotypic recurrent selection. There is very little knowledge on the inheritance of traits of agronomic relevance. Several approaches have been taken to overcome the constraints in the current methodologies for the genetic improvement of cassava. Evaluations at early stages of selection allow for estimates of general combining ability effect or breeding values of parental lines. Inbreeding by sequential self-pollination facilitates the identification of useful recessive traits, either already present in the Manihot gene pool or induced by mutagenesis.     

Inheritance of deeper root length and grain yield in half-diallel durum wheat (Triticum durum) crosses

Inheritance, heterosis and combining ability of deeper root length (DRL) and grain yield (GY) were investigated in durum wheat populations obtained from half‐diallel crossings among five parental lines differing in their DRL and GY. The study was conducted with the final objective of identifying parent lines to be used in a breeding programme to develop drought‐tolerant wheat varieties. General combining ability and specific combining ability effects were significant for both traits; however, additive gene effects were predominant over non‐additive effects. Partial dominance was ambidirectional for DRL and unidirectional for GY. Lines INRAT69 and Omrabia conferred DRL whereas Omrabia and Khiar transmitted high GY to their respective progenies. In the studied material, both characters were controlled mainly by dominant alleles, but they could also be attributed to recessive alleles although less frequently. Both broad‐sense and strict‐sense heritabilities were high for DRL, confirming the importance of additive gene effects, whereas strict‐sense heritability for GY was average, indicating the importance of interaction effects as compared with the additive effects; this could mean reduced selection efficiency for the latter trait. Thus, the expected genetic progress per cycle of selection will be lower for GY compared with DRL. Omrabia should be included in the breeding programme as a parent so that while maintaining high GY, resulting progeny should be better able to resist drought through DRL.     

花椰菜主要经济性状的配合力及遗传效应研究

采用Griffing 6×6完全双列杂交设计,对长江流域内秋冬栽培的6个主要花椰菜（Brassica oleraceaLinn.var.botrytis Linn.）资源的自交系育种材料的球高、球径、单球重、成熟期、毛花率和内叶盖球度等6个花球主要经济性状进行一般配合力（GCA）和特殊配合力（SCA）分析,并对花椰菜的各个性状进行了遗传相关性分析。结果表明：花椰菜的6个经济性状同时受加性和非加性效应控制。其中成熟期、毛花率、球高和内叶盖球度性状的一般配合力大于特殊配合力,受加性基因效应影响大;而球径、单球重等性状间一般配合力小于特殊配合力,在相当程度上受非加性基因控制。花椰菜各性状的狭义遗传力由大到小依次为：成熟期、毛花率、内叶盖球度、球高、球径和单球重。花椰菜的球高与单球重、球径与单球重、球高与成熟期、单球重与内叶盖球度、成熟期与内叶盖球度等5个成对性状应该同时选择;而球高与毛花率、球高与内叶盖球度、球径与成熟期、球径与毛花率、单球重与毛花率、成熟期与毛花率、毛花率与内叶盖球度等7个成对性状的选择可以独立进行,彼此间不会相互影响,可实现同一组合或品种具备多种优质性状。在6个自交系中,P2和P5是理想亲本;P4是配制耐寒组合的亲本材料;亲本P6应用价值最低。组合中表现最好的为P2×P4,各性状的特殊配合力均较优。     

Rice (<i>Oryza sativa</i> L.) Breeding among Hassawi Landrace and Egyptian Genotypes for Stem Borer (<i>Chilo agamemnon</i> Bles.) Resistance and Related Quantitative Traits

Rice stem borer (Chilo agamemnon Bles.) is a primary insect pest of rice and is a major limiting factor to rice production. Breeding for insect-resistant crop varieties has been an economic way of integrated pest management (IPM) as it offers a viable and ecologically acceptable approach. This study was aimed to evaluate rice genotypes for their resistance against rice stem borer. Seven parental genotypes with twenty one F1 crosses were evaluated for genotypic variation in field experiments. Analysis of variance revealed significant differences for the studied traits in almost all crosses and parents. In addition, the mean squares of parents versus their crosses were signifi- cant for stem borer resistance and other associated traits. Moreover, both general combining ability (GCA) and specific combining ability (SCA) variances were highly significant for all characters studied in the F1 generation. Based on GCA, 4 genotypes (Sakha101, Gz6903-3-4-2-1, Gz9577-4-1-1 and Hassawi) exhibited highly significant negative values for stem borer resistance (–0.53, –1.06, –0.18 and –0.49, respectively) indicating they are the best combiners for stem borer resistance. Based on SCA analysis, nine cross combinations showed highly significant negative effects for stem borer resistance. Similarly, the cross Giza178 Hassawi was the best combination with significantly highest value for early maturity. In addition, seven crosses showed highly significant negative SCA for plant height trait. On the other hand, for panicle length, number of primary branches/panicle, panicle weight and 1000-grain weight, seven, four, eight and six crosses showed highly significant positive SCA, respectively. The result further revealed that the non-additive dominance genetic variance was higher than the additive variance for all evaluated traits indicating that non-additive genetic variances have a role in their inheritance. The broad-sense heritability estimates were high for all the studied traits. The stem borer resistance was significantly correlated with panicle weight and 1000-grain weight, which also showed a highly significant correlation with grain yield/plant. Thus these traits can be effectively employed in a breeding program to confer resistance against stem borer infestation in rice. It was further supported by biplot analysis, which clustered these potentially important traits into two quadrants showing their importance in any future breeding program to control stem borer infestation. This study has contributed valuable information for evaluation of genetic diversity in the local rice germplasm and its utilization in futuristic rice genetic improvement programs.     

A general approach for the study of a population of testcross progenies and consequences for recurrent selection

Summary A model to study genetic effects at the level of a population of testcross progenies is presented. As there is no dominance for the testcross value, with the restriction of epistasis to pairs of loci, only additive x additive epistasis can contribute to the variance among progenies. To estimate the variance among progenies due to epistasis, it is necessary to have the population structured in families of full sibs, half sibs or S₁, with only a few plants per family tested in combination with the tester. Using a two-way mating design to produce the families, it is possible to estimate the variance due to additive x additive epistasis. The consequence of the presence of epistasis is studied at the level of recurrent selection for combining ability with the tester. It seems that epistasis itself does not change the efficiency of the breeding methods considered. However, when the population from intercrossing is structured in families, it could be efficient to use a combined selection when the heritability is very low. In this case it would be efficient to produce full-sib families (by single-pair matings) at the level of intercrossing. The best procedure is to produce such families at the same time as crossing with the tester. In comparison to the classical scheme of selection for combining ability with a tester, such a modification increases the efficiency of selection 41.1% if an off-season generation can be used.     

甘蔗常用亲本及杂交组合家系评价

为评价我国甘蔗亲本的遗传特点和组合的选配效果,采用澳大利亚家系试验法,借助R软件估算亲本的遗传方差、一般配合力(GCA)和组合特殊配合力(SCA)。结果表明:锤度的遗传主要受母本加性基因效应所制约,蔗茎产量主要受母本加性基因效应和非加性基因效应所制约,株高、茎径和有效茎受父母本加性基因效应和非加性基因效应所制约。CP88-2143、ROC10、ROC26、桂糖00-122、粤糖00-318和云蔗99-113作母本,内江57-416、崖城93-26、粤糖91-976和粤糖00-319作父本杂交后代表现出高产高糖,可作为糖能兼用好亲本使用。根据组合特殊配合力效应(SCA),CP88-2143×粤糖00-319、ROC10×粤糖91-976、ROC26×崖城93-26、桂糖00-122×ROC22、粤糖91-976×ROC22、粤糖93-159×内江57-416和云蔗99-113×CP84-1198组合综合表现良好,可作为生产性杂交组合,加大力度使用。     

The resistance and tolerance of different cocoa varieties to cocoa swollen-shoot virus in Ghana

The resistance and tolerance to infection with cocoa swollen-shoot virus (virulent strain A) of forty-five and thirty-eight cocoa progenies respectively was estimated using a manual inoculation method. Resistance was estimated from the proportion of inoculated seedlings which developed symptoms, and tolerance from the severity of these symptoms during a 4-month period. Resistance was found among Nanay, Iquitos and Scavina, all Upper Amazon types; and an inter-Nanay cross was outstandingly resistant and offers scope for improvement by breeding. Some Amazon-Amazon and Trinitario-Amazon progenies snowed tolerance, especially those with Trinitario T9/21 as a parent. Some progenies seem sufficiently promising for field testing to select varieties suitable for planting in those areas in Ghana where swollen-shoot disease is epidemic.