The integrated concept of disease resistance; a new view including horizontal and vertical resistance in plants

Horizontal, uniform, race-non-specific or stable resistance can be discerned according to Van der Plank, from vertical, differential, race-specific or unstable resistance by a test in which a number of host genotypes (cultivars or clones) are tested against a number of pathogen genetypes traces of isolatest. If the total non-environmental variance in levels of resistance is due to main effects only differences between cultivars and differences between isolates) the resistance and the pathogen many (in the broad sense) are horizontal in nature. Vertical resistance and pathogenicity are characterized by the interaction between host and pathogen showing up as a variance compenent in this test due to interaction between cultivars and isolates. A host and pathogen model was made in which resistance and pathogenicity are governed by live polygenic loci. Within the host the resistance genes show additivity. Two models were investigated in model I resistance and pathogenicity genes operate in an additive way as envisaged by Van der Plank in his horizontal resistance. Model II is characterized by a gene-for-gene action between the polygenes of the host and those of the pathogen. The cultivar isolate test in model I showed only main effect variance. Surprisingly, the variance in model II was also largely due to main effects. The contribution of the interaction to the variance uppeared so small, that it would be difficult to discern it from a normal error variance. So-called horizontal resistance can therefore be explained by a polygenic resistance, where the individual genes are vertical and operating on a gene-for-gene basis with virulence genes in the pathogen. The data reported so far support the idea that model II rather than model I is the realistic one. The two models also revealed that populations with a polygenic resistance based on the gene-for-gene action have an increased level of resistance compared with the addition model, while its stability as far as mutability of the pathogen is concerned, is higher compared to those with an additive gene action. Mathematical studies of Mode too support the gene-for-gene concept. The operation of all resistance and virulence genes in a natural population is therefore seen as one integrated system. All genes for true resistance in the host population, whether they are major or minor genes are considered to interact in a gene-for-gene way with virulence genes either major or minor, in the pathogen population. The models revealed other important aspects. Populations with a polygenic resistance based on a gene-for-gene action have an increased level of resistance compared to populations following the addition model. The stability, as far as mutability of the pathogen is concerned, is higher in the interaction model than in the addition model. The effect of a resistance gene on the level of resistance of the population consists of its effect on a single plant times its gene frequency in the population. Due to the adaptive forces in both the host and the pathogen population and the gene-for-gene nature of the gene action an equilibrium develops that allows all resistance genes to remain effective although their corresponding virulence genes are present. The frequencies of the resistance and virulence genes are such that the effective frequencies of resistance genes tend to be negatively related to the magnitude of the gene effect. This explains why major genes often occur at low frequencies, while minor genes appear to be frequent. It is in this way that the host and the pathogen, both as extremely variable and vigorous populations, can co-exist. Horizontal and vertical resistance as meant by Van der Plank therefore do not represent different kinds of resistances, they represent merely polygenic and oligogenic resistances resp. In both situations the individual host genes interact specifically with virulence genes in the pathogen. Van der Plank's test for horizontal resistance appears to be a simple and sound way to test for polygenic inheritance of resistance. The practical considerations have been discussed. The agro-ecosystems should be made as diverse as possible. Multilines, polygenic resistance, tolerance, gene deployment and other measures should be employed, if possible in combination

Breeding potential of the basmati rice germplasm under water stress condition

Eight parents were selected on the basis of phenotypic and genotypic screening for the development of F1. All the possible combinations were made between the parents excluding reciprocals in diallel mating design. Data were analyzed by using Hayman graphical approach and Griffing’s approach to study the genetics of the parents and their F1 hybrids. Based on the genetic component analysis, both additive and non-additive components appeared which is important in the inheritance of most of the traits. Both additive and dominance type of gene action were found important in inheritance for different traits under study. Most of the traits showed constant gene action in both environments, but the gene action of some traits was affected by the environment. Morphological traits like plant height, productive tillers per plant and 1000 seed weight showed over dominance type of gene action in both environments (control and drought environments), while seeds per panicle and seed length width ratio showed this type of gene action only in drought conditions. The seeds per panicle and length width ratio showed additive type of gene action with partial dominance only in normal irrigation conditions. From Griffing analysis, genotypes CB-17, CB-32 and Basmati-198 were found to be good general combiners for productive tillers per plant, primary branches per panicle and yield per plant, especially under water stress condition. Also, maximum specific combining ability was found in Basmati-198 × CB-17 for productive tillers per plant, Basmati-198 × CB-42 for primary branches per panicle and CB-32 × CB-14 for yield per plant.Key words: Oryza sativa L., gene action, combining ability, stress, yield traits

Biochemical genetics

The field under review is growing so rapidly that it is impossible to cover more than a sampling of recent papers in the allotted space. Important subjects such as the genetics and chemistry of viruses and certain topics in bacterial genetics have had to be omitted, while others have not received the treatment they deserve. Studies of a primarily biochemical nature in which mutants have been employed as tools have been reviewed, as is customary, although it is recognized that their genetic interest lies chiefly in their providing materials for the further study of gene action

Optimal selection of sib pairs from random samples for linkage analysis of a QTL using the EDAC test

Percentages of extremely concordant and extremely discordant sib pairs are calculated that maximize the power to detect a quantitative trait locus (QTL) under a variety of circumstances using the EDAC test. We assume a large fixed number of randomly sampled sib pairs, such as one would hope to find in the large twin registries, and limited resources to genotype a certain number of selected sib pairs. Our aim is to investigate whether optimal selection can be achieved when prior knowledge concerning the QTL gene action, QTL allele frequency, QTL effect size, and background (residual) sib correlation is limited or absent. To this end we calculate the best selection percentages for a large number of models, which differ in QTL gene action allele frequency, background correlation, and QTL effect size. By averaging these percentages over gene action, over allele frequency, over gene action, and over allele frequencies, we arrive at general recommendations concerning selection percentages. The soundness of these recommendations is subsequently in a number of test cases

Identifikasi Aksi Gen Epistasis pada Toleransi Kedelai terhadap Cekaman Aluminium

The efectiveness of selection depends on the gene action cotrolling the character. The presence of epistatic gene action will delay the genetic gain in self pollinated crops like soybean. The objective of this research was to obtain information on genetic control of soybean tolerance to aluminum toxicity on nutrient culture. This research was conducted at green house of the University Farm IPB Cikabayan, Bogor, from April to June 2013. This research used 120 seedlings of F2 population generated from crossing between Argomulyo (Al-sensitive) with Tanggamus (Al-tolerant). Seedlings were grown in nutrient culture for 14 days with Al concentration of 1.5 mM and pH 4.0, to observe the vegetative growth under aluminum stress condition. The result showed that mean of roots length, shoot length, shoot to root ratio, wet and dry weight of root and shoot exceeded both parents mean value with moderate to high heritability. All observed characters had continue distribution pattern, and controlled by many genes. Duplicate epistasis additive gene action controlled only root length while other characters were controlled by complementary epistasis gene action

Studies on combining ability and gene action for yield and quality traits in Baby corn (Zea mays L.)

An investigation was carried out to assess the combining ability and nature of gene action in baby corn (Zea mays L.) genotypes, by making crosses of eight inbred lines namely, HKI 3209, SML 1, EC 595979, CM 128, VQL 1, G 18 seq C5 F 76-2-2-1-1-2-BBB, HKI 209, in diallel mating design (without reciprocal crosses) by following Griffing Model–I and Method–II during rabi season 2013-14 at the experimental farm of BAC, Sabour, Bhagalpur (Bihar). The crosses were evaluated in a randomized complete block design (RCBD) to assess the combining ability and nature of gene action. Based on general combining ability, parents CM 128 and VQL 1 were best parent forbreeding programme for yield and quality improvement. The specific combining ability also indicates that hybrid CM128 x VQL1 was best specific combiner for baby corn yield (4.11q/ha), fodder yield (50.91q/ha) as well as for better quality. The crosses CM 128 x HKI 209 recorded the high mean (7.35%) and SCA effects (2.57 ºBrix) for quality traits. The gene action analysis also revealed preponderance of non-additive gene action for yield and its contributing characters

Implication of Gene Action and Heritability Under Stress and Control Conditions for Selection Iron Toxicity Tolerant in Rice

Iron toxicity is major constraint of rice production in irrigated-lowland of tropical regions. Improvement the tolerance of the rice cultivar to iron toxicity needs the information some genetics parameters of the selected characters. Here we study the estimation of gene action and heritability of the grain yield and its component under iron-toxic stress and control field conditions in rice. The iron-toxic tolerant rice cultivars, Pokkali and Mahsuri were crossed with the sensitive cultivar, Inpara5 to develop six generation populations. The breeding materials were grown in the iron toxicity site and control in Taman Bogo, Lampung Indonesia. The sensitive parent and BC1P1 had lower stress tolerance index (STI) compared to the tolerant parent F1, F2 and BC1P2. Most of the characters including the grain yield were fitted the best model in five parameters which were more prominent with interactive epistasis of duplicate and complementary gene action. The heritability's under control were more higher compared to iron toxicity stress condition. Delaying selection to later generations and combining with the shuttle breeding between stressed and controlled environments were the best strategy for improving the grain yield and tolerance to iron toxicity in rice

Gene action controlling stability and adaptability in maize

Limited knowledge about the genetic merit of maize landraces contributes to their little use in breeding, al-though some reports pointed them as a source of useful alleles. Repeated cultivation of landraces for many generations could make them a useful germplasm source to enhance yield stability. This study pretends to determine if such statement holds, and to analyze stability in terms of gene action involved. Twenty Argentine landraces were testcrossed to three US and two Argentine elite lines, and evaluated in 13 environments. Effects of general and specific combining ability for grain yield and ecovalence, as well as for regression coefficients of response to environments were also predicted. Non-additivity resulted more important than additivity for controlling ecovalence, and frequently resulted detrimental to stability. Although landraces contributed to ecovalence, their importance was less than that of lines. Testcrosses ́ adaptability to environments was variable depending on the line tester considered. Relative greater importance of lines ́ general combining ability for ecovalence than landraces’ general combining ability could be attributed to a successful selection for stability during the development of inbred lines. Sixty percent of landraces appeared more adapted to unfavorable environment, which suggests their higher level of rusticity. Argentine lines provided greater stability to their testcrosses than US lines. Correlation between grain yield and stability was mainly dependent upon non additive effects. More productive testcrosses tend to have greater ecovalence (less stability) due to specific combining ability effects. Inbred lines selected for greater general combining ability effect tend to provide their estcrosses higher stability.EEA PergaminoFil: Eyherabide, Guillermo. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Pergamino; ArgentinaFil: Boca, Rosa Teresa. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Clima y Agua; ArgentinaFil: Lopez, César. Universidad Nacional de Lomas de Zamora. Facultad de Ciencias Agrarias; Argentin

Line x testers analysis of tropical maize inbred lines under heat stress for grain yield and secondary traits

The combining ability and mode of gene action in tropical maize germplasm is not extensively studied. In the present study, a line x tester analysis involving 290 test-cross hybrids developed by crossing 145 tropical maize inbred lines with two testers and four standard checks was conducted for grain yield and other agronomic traits under heat stress during summer 2013 at B gudi agriculture research station. The main objective of the investigation was to study mode of gene action governing the traits under heat stress along with identification of superior inbred lines based on combining ability to develop heat tolerant hybrids. Analysis of variance showed that mean squares for genotypes was highly significant for grain yield, days to anthesis and silking, anthesis silk interval, plant height and ear height under heat stress. The combining analysis for lines (GCA), tester (GCA) and line x tester (SCA) showed significant difference (P < 0.01) for all the traits under study except ASI for LXT interaction. This indicates that both additive and non additive gene action control the expression of these traits under heat stress. The low GCA variance to SCA variance ratio for all the traits showed preponderance of non-additive gene action in the inheritance of the traits. Among 145 inbred lines used for study, the inbreds L78, L73, and L37 showed good general combining ability for grain yield. The crosses L118 x L2 and L143 x L1 were having good specific combiners ability for grain yield under heat stress. These inbreds can be used in breeding program for development of heat tolerant hybrids through exploitation of dominant gene action