Stability of biochemical constituents and their relationships with resistance to shoot fly, Atherigona soccata (Rondani) in seedling sorghum

The stability of biochemical constituents and their association with resistance to shoot fly (Atherigona soccata Rondani) was evaluated for reducing sugars, total sugars, nitrogen, phosphorus, potassium, chlorophyll and moisture contents at weekly intervals of seedling growth (7, 14, 21 and 28 days after emergence) in 14 selected grain sorghum genotypes [five resistant accessions (IS nos. 1054, 2146, 2312, 3962 and 4664); three susceptible checks (CK 60B, CSV 1 and CSH 1); one national variety (CSV 8R); and five post-rainy advanced generation (F₆) breeding lines (148 × CS 3541, SPV 103 × IS 4664, CSV 8R × SPV 104, SPV 104 × M 35-1, and PD 3-1-11 derivative)]. The genotypes IS 2312 and IS 4664 showed stability of antixenosis for oviposition during post-rainy season advanced generation lines compared to the susceptible checks. Deadheart formation was low and the expression of resistance was stable across different seedling growth stages in IS 1054 and IS 2146. Depletion in levels of reducing sugars and phosphorus in resistant genotypes played a significant role in deadheart formation in the test genotypes. Positive association of nitrogen and potassium with oviposition at early seedling stages indicated their role in releasing chemical cues for oviposition. Low levels of reducing sugars and total sugars seemed to enhance the degree of resistance to sorghum shoot fly. The total chlorophyll content had no relationship with antixenosis for oviposition. No relationship was observed between moisture content of sorghum seedlings and shoot fly resistance. Low concentrations of reducing sugars, total sugars, nitrogen, phosphorus and potassium in sorghum seedlings greatly enhanced the degree of antixenosis for oviposition/feeding and deadheart formation, and can be used as selection criteria for resistance to shoot fly.     

Relative susceptibility of different male-sterile cytoplasms in sorghum to shoot fly, <Emphasis Type="Italic">Atherigona soccata</Emphasis>

Summary The shoot fly, Atherigona soccata is an important pest of sorghum, and host plant resistance is one of the most effective components for managing this pest. Most of the hybrids grown in India based on milo cytoplasm (A₁ cytoplasm) are highly susceptible to shoot fly. Therefore, the present studies were undertaken to evaluate different male-sterile cytoplasms (CMS) for their relative susceptibility to sorghum shoot fly. Oviposition and deadheart formation were significantly lower on the maintainer lines as compared to the corresponding male-sterile lines. Among the cytoplasms tested, A₄M cytoplasm showed antixenosis for oviposition and suffered lower deadheart formation than the other cytoplasms tested. The A₄G₁ and A₄M cytoplasms suffered lower deadhearts in tillers than the other cytoplasms. Recovery following shoot fly damage in A₄M, A₃, and A₂ cytoplasms was better than in the other cytoplasms tested. The larval and pupal periods were longer and male and female pupal weights lower in A₄M and A₄VzM CMS backgrounds compared to the other CMS systems. Fecundity and antibiosis indices on CMS lines were lower than on the B-lines. The A₄M cytoplasm was found to be relatively resistant to sorghum shoot fly, and can be exploited for developing shoot fly-resistant hybrids for sustainable crop production in future.     

Mechanisms of resistance to shoot fly, <Emphasis Type="Italic">Atherigona soccata</Emphasis> in sorghum

Summary Sorghum shoot fly, Atherigona soccata (Rondani) is an important pest of sorghum in Asia, Africa, and Mediterranean Europe, and host plant resistance is an important component for the management of this pest. The levels of resistance in the cultivated germplasm are low to moderate, and therefore, it is important to identify genotypes with different mechanisms of resistance to pyramid the resistance genes. We studied the antixenosis for oviposition, antibiosis, and tolerance components of resistance in a diverse array of shoot fly-resistant and -susceptible genotypes. The main plants and tillers of SFCR 151, ICSV 705, SFCR 125, and, IS 18551 experienced lower shoot fly deadhearts at 28 days after seedling emergence, produced more number of productive tillers. The insects fed on these genotypes also exhibited longer larval period (10.1–11.0 days compared to 9.3 days on Swarna), lower larval survival and adult emergence (54.7–67.8 and 46.7–52.2% compared to 73.3 and 60.6% on Swarna, respectively), and lower growth and adult emergence indices as compared to the susceptible check, Swarna. Physico-chemical traits such as leaf glossiness, trichome density, and plumule and leaf sheath pigmentation were found to be associated with resistance, and chlorophyll content, leaf surface wetness, seedling vigor, and waxy bloom with susceptibility to shoot fly and explained 88.5% of the total variation in deadhearts. Step-wise regression indicated that 90.4% of the total variation in deadhearts was due to leaf glossiness and trichome density. The direct and indirect effects, correlation coefficients, multiple and step-wise regression analysis suggested that deadhearts, plants with eggs, leaf glossiness, trichomes on the abaxial surface of the leaf, and leaf sheath pigmentation can be used as marker traits to select for resistance to shoot fly, A. soccata in sorghum.     

A genetic study of popping quality in Sorghum (Sorghum bicolor (L.) Moench)

Summary Two crosses of sorghum, Sorghum bicolor (L.) Moench (IS 1054 × ICSV-1, and IS 5604 × IS 1054) were evaluated in parental, F1, F2, and backcross generations for the variation in their popping quality as measured by pop volume (ml). Dominance was in the direction of low pop volume. Dominance and additive gene effects, in that order, governed most of the variation, while significant dominance x dominance type of interaction effects could also be detected. There was no evidence for higher order gene interactions.Approved as Journal Article 630 by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru, P.O. 502 324, Andhra Pradesh, India.     

Inheritance of resistance to spotted stem borer, Chilo partellus, in sorghum, Sorghum bicolor

The spotted stem borer, Chilo partellus, is one of the most important pests of sorghum, and host plant resistance is an important component for the management of this pest. Most of the sorghum hybrids currently under cultivation are based on cytoplasmic male-sterility (CMS). In order to develop a strategy for resistance to stem borer, we studied the traits associated with resistance, and their nature of gene action in F₁ hybrids derived from resistant, moderately resistant, and susceptible CMS and restorer lines. The hybrids based on stem borer-resistant, moderately resistant, or susceptible CMS and restorer lines were equally resistant or susceptible as the parents for leaf feeding [Damage rating (DR) 5.8 to 6.6 vs. 5.9 to 6.6], and had significant and decreasing trend in deadheart formation (resistant CMS × resistant restorer lines < moderately resistant CMS × moderately resistant restorer lines < susceptible CMS × susceptible restorer lines), respectively. Proportional contributions of restorer lines were greater than those of the CMS lines for leaf feeding, deadhearts, recovery and overall resistance, stalk length, nodes per plant, stem borer holes per plant, and peduncle tunneling. The general (GCA) and specific combining ability (SCA) estimates suggested that leaf feeding score, number of nodes, overall resistance score, panicle initiation, recovery score, and stalk length (dominance type of gene action) have been found to be associated with resistance to spotted stem borer, governed by additive type of gene action, their correlation and direct effects in the same direction, and explained 65.3% of the variation in deadhearts, and thus could be used as marker traits to select and breed for resistance to C. partellus in sorghum. The parents having significant SCA effects for two or more resistance traits for either or more parents have also been discussed for their use in the stem borer resistance breeding.     

Isolation and characterization of resistance gene analogs (RGAs) from sorghum (Sorghum bicolor L. Moench)

Degenerate primers designed based on known resistant genes (R-genes) and resistance gene analogs (RGAs) were used in combinations to elucidate RGAs from Sorghum bicolor, cultivar M 35-1. Most of the previously tried primer combinations resulted in amplicons of expected 500–600 bp sizes in sorghum along with few novel combinations. Restriction analysis of PCR amplicons of expected size revealed a group of fragments present in a single band indicating the heterogeneous nature of the amplicon. Many of these were cloned and some were considered for analysis. The nucleotide sequence of different cloned fragments was done and their predicted amino acid sequences compared to each other and to the amino acid sequences of known R-genes revealed significant sequence similarity. A cluster analysis based on neighbor-joining (N-J) method was carried out using sorghum RGAs (SRGAs) together with several analogous known R-genes resulting in two major groups; cluster-I comprising only SRGAs and cluster-II comprised of known R-gene sequences along with three SRGAs. Further analysis clearly indicated similarity of SRGAs in overall sense with already known ones from other crop plants. These sequences can be used as guidelines to detect, map and eventually isolate numerous R-genes in sorghum.     

Genetic analysis of biotype I greenbug resistance in sorghum

The greenbug has been a major insect pest of sorghum since 1968. Although sources of genetic resistance have been identified to combat this pest, new and virulent biotypes have successfully overcome these resistance genes. KS 97 was developed and released by the Kansas Agricultural Experiment Station as a new germplasm source of biotype I greenbug resistance in sorghum. The objectives of this study were to evaluate combining ability effects for greenbug resistance in KS 97 and to determine the number of genes responsible for this trait. Six inbred lines, including KS 97 and greenbug resistant and susceptible checks, were intercrossed using a Design-II mating scheme to produce nine F1 hybrids. Responses of seedlings of parent lines and hybrids to biotype I greenbug were evaluated in replicated growth chamber experiments. The results of these studies indicated significant effects of general combining ability (GCA) and specific combining ability (SCA). Greenbug resistance derived from KS 97 was found to be incompletely dominant, and the GCA effect for resistance associated with KS 97 was superior to that associated with PI550610, the resistant check. Segregation studies to determine the number of genes responsible for greenbug resistance in KS 97 were conducted in BC1F1 populations. KS 97 was introgressed into three greenbug-susceptible genetic backgrounds. Segregation analysis indicated a consistent 1:3 (resistant:susceptible) segregation ratio for greenbug resistance across populations. The simplest explanation for these results is that two dominant genes requiring complementary gene action control resistance. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic divergence among a non-restorer collection of sorghum (Sorghum bicolor (L.) Moench) and its relationship with heterosis

Summary A genetic diversity analysis in a collection of 171 non-restorer lines of sorghum (Sorghum bicolor (L.) Moench) using D² technique and canonical variate analysis indicated that considerable variation in grain yield has been added to the collection by the addition of lines derived from random mating populations. The efficiency of D² and canonical variate techniques in distinguishing extremely diverse genotypes was confirmed. However, the two techniques showed weak correspondence in their clusters. The F₁ hybrids of 15 diverse lines exhibited no relationship between heterosis or per se performance of crosses and diversity in their parents. Therefore, traditional plant breeding methods are being advocated.Approved by ICRISAT as Journal Article no. 435.     

Heritability estimates of variation for NaCl tolerance in Sorghum bicolor (L.) Moench seedlings

Summary Data on root lengths of two-week-old seedlings of 51 Sorghum bicolor (L.) Moench accessions germinated in 50, 100, 150, 175, and 200 mM NaCl solutions were used to estimate broad sense heritabilities of variation for salinity tolerance.Estimates of broad sense heritabilities ranged from 0.38 to 0.73, the highest being in 50 mM NaCl, suggesting that there is potential for improving salinity tolerance in the species through selection and breeding.     

Molecular Marker based Genetic Diversity Analysis in Rice (Oryza sativa L.) using RAPD and SSR markers

The availability of an array of molecular marker systems allowed comparing the efficiency of two of these marker systems to estimate the relationships among various taxa. The objective of this study was to assess the genetic diversity among 40 cultivated varieties and five wild relatives of rice, Oryza sativa L. involving simple sequence repeat (SSR) randomly amplified polymorphic DNA (RAPD) markers. The accessions were evaluated for polymorphisms after amplification with 36 decamer primers and 38 SSR primer pairs. A total of 499 RAPD markers were produced among the 40 cultivated varieties and five wild relatives with a polymorphism percentage of 90.0. Out of 38 SSR primer pairs used, only one locus viz., RM115 was monomorphic. The average Polymorphism Information Content (PIC) value was 0.578 and it ranged from a low of zero (RM 115) to a high of 0.890 (RM 202). The Mantel matrix correspondence test was used to compare the similarity matrices and the correlation coefficient was 0. 582. The test indicated that clusters produced based on RAPD and SSR markers were not conserved since matrix correlation value was 0.582 as against the minimum required value of 0.800. The two marker systems contrasted most notably in pair-by-pair comparisons of relationships. SSR analysis resulted in a more definitive separation of clusters of genotypes indicating a higher level of efficiency of SSR markers for the accurate determination of relationships between accessions that are too close to be accurately differentiated by RAPD markers. This revised version was published online in July 2006 with corrections to the Cover Date.     

Chromosome 1D as a possible location of a gene (s) controlling variation between wheat (Triticum aestivum L.) varieties for carbon isotope discrimination (Δ) under water-stress conditions

Cytoplasmic male-sterility (CMS) in pigeonpea has been reported when some wild relatives of pigeonpea were crossed as the female parent with cultivated types as the male parent. In this paper we report a new source of CMS developed by using the cultivated pigeonpea as the female parent and one of its wild relative Cajanus acutifolius as the pollen donor. This is the first report in pigeonpea where CMS has been developed using the cytoplasm of cultivated pigeonpea. Several pure line cultivars of pigeonpea restored pollen fertility whereas cv. HPL 24 partially maintained male-sterility. The wild species C. acutifolius used as one of the parents, maintained complete sterility. Cytological analysis revealed that both in male-sterile as well as the fertile floral buds, meiosis proceeded normally till the tetrad stage. However in the male-sterile genotypes during the formation of tetrads, the pollen mother cell (PMC) wall did not dissolve to release the tetrads unlike in the fertile genotypes and this major event was found to be responsible for male-sterility.     

Effect of cytoplasmic male-sterility in sorghum on host plant interaction with sorghum midge,Contarinia sorghicola

Summary Sorghum midge, Contarinia sorghicola Coq. (Diptera: Cecidomyiidae) is one of the most important pests of grain sorghum worldwide. We studied the reaction of midge-resistant and midge-susceptible genic-cytoplasmic male-sterile (A-lines) and their maintainers (B-lines), and the effect of resistant and susceptible restorers on sorghum midge. Midge damage and adult emergence were significantly lower on the B-lines of midge-resistant genotypes (PM 7061 and PM 7068) than their corresponding A-lines, while the reverse was true for the midge-susceptible genotypes (296A and ICSA 42). Differences in midge damage and the number of midges emerged were not significant between the midge-resistant and midge-susceptible A-lines when infested without pollination (except midge emergence on PM 7061A). Pollination with a midge-resistant restorer (DJ6541) reduced midge emergence significantly in one of two seasons. Source of pollen did not influence midge emergence on the highly-resistant A-line, PM 7061A. The implications of these observations in the development of midge-resistant hybrids were discussed.     

Characterization and genetic control of germination-emergence responses of grain sorghum to salinity

Summary When grain sorghum is grown in saline soils, one cause of low yield is poor crop establishment. The objectives of this study were to assess the response of grain sorghum to salinity in the germination-emergence stages, study the inheritance of salt tolerance at this stage, and determine the relative contribution to final emergence of salt effects during imbibition, and after onset of germination. Twelve inbred lines and 18 F1 hybrids, resulting from an incomplete 6×6 factorial mating design, were tested for germination and emergence in folded paper at 10 salt concentrations, from 1.8 to 36 dSm^-1. The mean EC₅₀ (the electrical conductivity at which the variable score declines by 50%) for emerged seedlings production was 21.2 dSm^-1. Large genotypic differences were observed for salt tolerance at germination and emergence stages, which were not related to the viability of seeds, and poorly related to seed weight (considered as an estimate of intrinsic seed vigor). In the hybrids, these differences were due to SCA and female GCA for emergence, and female GCA for germination, though the male GCA was also significant for both characters. Line per se performance was significantly correlated to individual GCA estimates for emergence, but not for germination. Heterosis was only detected in three crosses for final emergence and in one cross for germination. The genetic differences in final emergence were mainly due to effects occurring after the onset of germination rather than a consequence of effects during imbibition.     

Genes for scald resistance from wild barley (Hordeum vulgare ssp spontaneum) and their linkage to isozyme markers

Summary Accessions of Hordeum vulgare ssp. spontaneum, the wild progenitor of barley, collected in Israel (70), Iran (15) and Turkey (6) were screened for seedling response to four isolates of Rhynchosporium secalis, the pathogen causing leaf scald in barley. Resistance was very common in the collection (77%) particularly among accessions from the more mesic sites (90%). The genetics of this resistance were investigated in fifteen backcross (BC₃) lines that contained an isozyme variant from H.v. ssp. spontaneum in a H.v. ssp. vulgare (cv. Clipper) background and were resistant to scald. Segregation in the BC₃F₂ families conformed with a single dominant resistance gene in 9 of the 15 lines. Scald resistance and the isozyme marker were closely linked in three of the BC₃-lines, loosely linked in four and unlinked in the remaining eight. Scald resistance genes were identified on barley chromosomes 1, 3, 4 and 6. Crosses between several of the scald resistant BC-lines together with the linkage data indicated that at least five genetically independent resistances are available for combining together for deployment in barley. The linkage of scald resistance in several BC₃-lines to the isozyme locus Acp2 is of special interest as this locus is highly polymorphic in wild barley.     

QTL analysis and mapping of pre-harvest sprouting resistance in Sorghum

One of the most important agronomic problems in the production of sorghum [Sorghum bicolor (L.) Moench] in humid climates is pre-harvest sprouting (PHS). A molecular linkage map was developed using 112molecular markers in an F₂ mapping population derived from a cross between IS 9530 (high resistance to PHS) and Redland B2 (susceptible to PHS). Two year phenotypic data was obtained. By means of interval mapping analysis, two significant QTL were detected in two different linkage groups with LOD scores of 8.77and 4.39. Each of these two QTL individually explained approximately 53% of the phenotypic variance, but together, in a two-QTL model, they explained 83% of the phenotypic variance with a LOD score of 12.37.These results were corroborated by a one-way ANOVA in which the four flanking markers of the most likely QTL positions displayed highly significant values in theF-test, and significant variation in trait expression was associated with marker genotypic classes. The four markers with highest effect in the one-way ANOVA were also detected in the second year replication of the F₂ population, and significant genotype × environment interactions was observed. The putative relationship between PHS resistance in sorghum and the maize Vp1 gene is also discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Compensation in grain weight and volume in sorghum is associated with expression of resistance to sorghum midge, Stenodiplosis sorghicola

Sorghum midge, Stenodiplosis sorghicola (Coquillett) is one of the most important pests of grain sorghum worldwide. We studied the inheritance of resistance to sorghum midge and compensation in grain weight and volume in panicles of sorghum hybrids and their parents under uniform infestation (40 midges per panicle for two consecutive days). Sorghum midge damage ranged from 8.2 to 82.4% in the maintainer lines (B-lines) of the females parents (A-lines), and 9.0 to 67% in the male parents (restorer lines). Hybrids involving resistant × resistant parents were highly resistant, while those involving resistant ×susceptible and susceptible × resistant parents showed moderate susceptibility. Susceptible × susceptible hybrids were susceptible. Compensation in (percentage increase) grain weight and volume in midge-infested panicles of midge-resistant parents and their F₁ hybrids was greater than in midge-susceptible parents and hybrids. General combining ability effects for midge damage, and grain weight and volume were significant and negative for the midge-resistant females (ICSA 88019 and ICSA 88020), whereas those for the midge-susceptible females (ICSA 42 and 296A) were significant and positive. However, the reverse was true in case of compensation in grain weight and volume. Inheritance of compensation in grain weight and volume and resistance to sorghum midge is controlled by quantitative gene action with some cytoplasmic effects. Resistance is needed in both parents to realize full potential of midge-resistant hybrids. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evaluation of greenhouse inoculation techniques to screen sorghum for resistance to downy mildew

Summary Six inoculation techniques were compared for the artificial promotion of downy mildew (Peronosclerospora sorghi) in sorghum. These were (1) sprouted seeds incubated between sporulating infected leaves, (2) sprouted seeds depped in conidial suspension, (3) sprouted seeds sprayed with conidial suspension, (4) seedlings at plumule stage inoculated with drops of a conidial suspension, (5) seedlings at plumule stage sprayed with a conidial suspension, and (6) seedling showered with conidia falling from infected leaves. Seedlings at the one-leaf stage sprayed with a conidial suspension (6 × 10⁵ ml^-1) showed the highest systemic infection (100%) in the susceptible lines IS 643 and IS 18433. This technique is effective, repeatable, and allows the deposition of a conidial suspension as a fine mist on the entire seedling surface. In the greenhouse, the technique was used to test the downy mildew reaction of genotypes previously reported as resistant (< 5% incidence) in 3–4 years of field screenings. Of the 61 genotypes tested, 21 were free from downy mildew, 14 had less than 5% incidence, and the rest showed variable susceptible reactions. Therefore, the technique can be reliably and effectively used in the greenhouse to detect disease escapes and to indentify resistance.     

Mechanisms and diversity of resistance to sorghum midge, Stenodiplosis sorghicola in Sorghum bicolor

Sorghum midge, Stenodiplosis sorghicola (Coquillett) is the most important pest of grain sorghum worldwide, and plant resistance is an important component for the control of this pest. To identify sorghum genotypes with diverse mechanisms of resistance to sorghum midge, we studied oviposition, larval survival, and midge damage in 27 sorghum midge-resistant genotypes, and a susceptible check under greenhouse conditions. Observations were also recorded on floral characteristics and compensation in grain mass. Of the 28 sorghum genotypes tested, 19 showed high levels of antixenosis to oviposition as a component of resistance, and had <20% spikelets with eggs when infested with 10 or 25 sorghum midge females per panicle under no-choice conditions in the headcage. Genotypes IS 8887, IS 10712, IS 21873, IS 21881, ICSV745, and QL 39 showed antibiosis as one of the components of resistance. Lines IS 7005, IS 10712, IS 18563, IS 21873, IS 21881, PM 15936-2,ICSV 197, and ICSV 745 showed <20% spikelets with eggs, larvae,or, midge damaged chaffy spikelets across infestation levels, compared with >80% midge damaged spikelets in QL 12 - the susceptible check. Genotypes showing resistance to sorghum midge have smaller glumes than the susceptible check, QL 12. However, IS 7005, IS 18653, and ICSV745 have relatively large sized glumes, but suffered <20% midge damage suggesting that factors other than glume size also contribute to midge resistance in sorghum. Fourteen genotypes showed >20% compensation in grain mass when the panicles were reduced to 250 spikelets and infested with 10 or 25 midges per panicle. There is considerable diversity in sorghum genotypes showing resistance to sorghum midge. Genotypes with diverse combination of characteristics associated with resistance to sorghum midge can be used in breeding programs to broaden the genetic base and increase the levels of resistance to this insect. This revised version was published online in August 2006 with corrections to the Cover Date.     

Inheritance of resistance to head bugs and its interaction with grain molds in Sorghum bicolor

Sorghum head bug, Calocoris angustatus Lethiery is one of the most important pests of grain sorghum in India. Head bug damage increases the severity of grain molds, which renders the grain unfit for human consumption. Therefore, we studied the gene action for resistance to head bugs and grain molds in a diverse array of male-sterile lines and testers in a line × tester mating design under natural infestation. Mean squares for parents, parents vs crosses, lines, testers, and lines × testers were significant for head bug damage and grain mold severity. General combining ability (GCA) effects were significant and negative for ICSA 88019 for head bug damage, and ICSA 88019 and ICSA 88020 for grain molds (except for ICSA 88020 in 1993). General combining ability effects were positive for ICSA 42 and 296 A. GCA effects of lines and testers for head bug damage and grain mold severity were in the same direction (+ve or −ve). Head bug damage in the grain was significantly correlated with grain mold severity. Testers IS 8891, IS 15107, and TAM 2566 (with colored grain and less susceptibility to molds) produced mold-resistant hybrids in combination with all the male-sterile lines, while the reverse was true in the case of Swarna and ICSV 112. Resistance to head bugs showed dominance to partial dominance type of gene action, while in the case of grain molds, it showed dominance to over dominance. Resistance to these pests is governed by both additive and nonadditive types of gene action. The implications of these results are discussed in relation to need for crop improvement in sorghum. This revised version was published online in July 2006 with corrections to the Cover Date.