Panicle Compactness Research Articles

Panicle compactness along with abiotic factors influence the abundance of earhead feeding insect pests of sorghum [Sorghum bicolor (L.) Moench]

Panicle compactness along with abiotic factors influence the abundance of earhead feeding insect pests of sorghum [Sorghum bicolor (L.) Moench]

Analyzing the variability parameters of the landraces and varieties of little millet (Panicum sumatrense Roth ex Roem. & Schult.)

Little millet is one of the underutilized crops among the cereals, which is being cultivated by farmers of tribal  agriculture. The landraces under cultivation possess excellent variability presenting good opportunities for selection. In view of this, the current study was carried out with 17 little millet landraces for 10 quantitative and nine qualitative traits. The study revealed the preponderance of additive gene action for all the 10 traits and hence effective selection could be done for their improvement. Higher to moderate ranges for PCV and GCV with minimum ECV for genetic variability for all the traits were observed. Among the nine qualitative traits, there were significant variations observed for inflorescence shape and panicle compactness. Hence, these traits could be utilized as major DUS descriptors in differentiating the little millet landraces in future. Further the PCA analysis exhibited three reliable principal components contributing to an overall variation of 74.54%. The traits such as days to 50% flowering, peduncle length and flag leaf length were the major positive contributors for variability across all the eigen vectors. These traits were found to exhibit a higher variability among the population and thus a rewarding selection and hybridization for improving these traits could be effected in future breeding programs. Among all the landraces, chitta samai, perunsamai, ATL 1, CO 4 (samai), paakulam karunjamai and vellai samai could be further identified as desirable donors for improving the yield parameters in little millet breeding programs in future. Keywords: Little millet, landraces, GCV, PCV, heritability, genetic advance, PCA

Combining ability studies of grain Fe and Zn contents of pearl millet (Pennisetum glaucum L.) in West Africa.

Micronutrient malnutrition is a major challenge in Africa, where half a million children die each year because of lack of micronutrients in their food. Pearl millet is an important food and fodder crop for the people living in the Semi-Arid regions of West Africa. The present study was conducted to determine the stability, combining ability, and gene action conditions of the high level of Fe and Zn content in grain and selected agronomic traits. Hence, eight genotypes were selected based on the availability of grain Fe and Zn contents and crossed in a full diallel mating design. Progenies from an 8 × 8 diallel mating along with the parents were evaluated in an alpha lattice design with three replications in three locations for two years. The parental lines Jirani, LCIC 9702 and MORO, had positive significant general combining ability (GCA) effects for grain Fe concentration, while Jirani and MORO had positive significant GCA effects for grain Zn concentration. For the specific combining ability (SCA), among the 56 hybrids evaluated, only the hybrids LCIC 9702 × Jirani and MORO × ZANGO had positive significant SCA effects for grain Fe concentration across locations, and for grain Zn concentration, the hybrids Gamoji × MORO, LCIC 9702 × Jirani, and ICMV 167006 × Jirani had positive significant SCA effects. The reciprocal effects were significant for grain Zn concentration, grain yield, flowering time, plant height, test weight, and downy mildew incidence, suggesting that the choice of a female or male parent is critical in hybrid production. Grain Fe and Zn concentration, flowering time, plant height, panicle length, panicle girth, panicle compactness, and downy mildew incidence were found to be predominantly under additive gene action, while grain yield and test weight were predominantly under non-additive gene action. A highly positive correlation was found between grain Fe and Zn concentrations, which implies that improving grain Fe trait automatically improves the grain Zn content. The stability analysis revealed that the hybrid ICMV 167006 × Jirani was the most stable and high-yielding with a high level of grain Fe and Zn micronutrients.

Effect of Panicle Morphology on Grain Filling and Rice Yield: Genetic Control and Molecular Regulation.

The demand for rice is likely to increase approximately 1.5 times by the year 2050. In contrast, the rice production is stagnant since the past decade as the ongoing rice breeding program is unable to increase the production further, primarily because of the problem in grain filling. Investigations have revealed several reasons for poor filling of the grains in the inferior spikelets of the compact panicle, which are otherwise genetically competent to develop into well-filled grains. Among these, the important reasons are 1) poor activities of the starch biosynthesizing enzymes, 2) high ethylene production leading to inhibition in expressions of the starch biosynthesizing enzymes, 3) insufficient division of the endosperm cells and endoreduplication of their nuclei, 4) low accumulation of cytokinins and indole-3-acetic acid (IAA) that promote grain filling, and 5) altered expressions of the miRNAs unfavorable for grain filling. At the genetic level, several genes/QTLs linked to the yield traits have been identified, but the information so far has not been put into perspective toward increasing the rice production. Keeping in view the genetic competency of the inferior spikelets to develop into well-filled grains and based on the findings from the recent research studies, improving grain filling in these spikelets seems plausible through the following biotechnological interventions: 1) spikelet-specific knockdown of the genes involved in ethylene synthesis and overexpression of β-CAS (β-cyanoalanine) for enhanced scavenging of CN− formed as a byproduct of ethylene biosynthesis; 2) designing molecular means for increased accumulation of cytokinins, abscisic acid (ABA), and IAA in the caryopses; 3) manipulation of expression of the transcription factors like MYC and OsbZIP58 to drive the expression of the starch biosynthesizing enzymes; 4) spikelet-specific overexpression of the cyclins like CycB;1 and CycH;1 for promoting endosperm cell division; and 5) the targeted increase in accumulation of ABA in the straw during the grain filling stage for increased carbon resource remobilization to the grains. Identification of genes determining panicle compactness could also lead to an increase in rice yield through conversion of a compact-panicle into a lax/open one. These efforts have the ability to increase rice production by as much as 30%, which could be more than the set production target by the year 2050.

Genes determining panicle morphology and grain quality in rice (Oryza sativa).

The world's increase in rice (Oryza sativa L.) production is not keeping up with the increase in its population. To boost the introduction of new high-yielding cultivars, knowledge is being gained on the genes and quantitative trait loci (QTLs) determining the panicle phenotype. The important are those determining yield of the crop, such as grain numbers per panicle and size and weight of the grains. Biochemical and molecular functions of many of them are understood in some details. Among these, OsCKX2 and OsSPL14 have been shown to increase panicle branching and grain numbers when overexpressed. Furthermore, miRNAs appear to play an important role in determining the panicle morphology by regulating the expressions of the genes like OsSPL14 and GRF4 involved in panicle branching and grain numbers and length. Mutations also greatly influence the grain shape and size. However, the information gained so far on the genetic regulation of grain filling and panicle morphology has not been successfully put into commercial application. Furthermore, the identification of the gene(s)/QTLs regulating panicle compactness is still lacking, which may enable the researchers to convert a compact-panicle cultivar into a lax/open one, and thereby increasing the chances of enhancing the yield of a desired compact-panicle cultivar obtained by the breeding effort.

Genome-Wide Association Mapping Identifies Novel Panicle Morphology Loci and Candidate Genes in Sorghum.

Panicle morphology is an important trait in racial classification and can determine grain yield and other agronomic traits in sorghum. In this study, we performed association mapping of panicle length, panicle width, panicle compactness, and peduncle recurving in the sorghum mini core panel measured in multiple environments with 6,094,317 single nucleotide polymorphism (SNP) markers. We mapped one locus each on chromosomes 7 and 9 to recurving peduncles and eight loci for panicle length, panicle width, and panicle compactness. Because panicle length was positively correlated with panicle width, all loci for panicle length and width were colocalized. Among the eight loci, two each were on chromosomes 1, 2, and 6, and one each on chromosomes 8 and 10. The two loci on chromosome 2, i.e., Pm 2-1 and Pm 2-2, were detected in 7 and 5 out of 11 testing environments, respectively. Pm 2-2 colocalized with panicle compactness. Candidate genes were identified from both loci. The rice Erect Panicle2 (EP2) ortholog was among the candidate genes in Pm 2-2. EP2 regulates panicle erectness and panicle length in rice and encodes a novel plant-specific protein with unknown functions. The results of this study may facilitate the molecular identification of panicle morphology-related genes and the enhancement of yield and adaptation in sorghum.

Identification of novel QTLs for grain fertility and associated traits to decipher poor grain filling of basal spikelets in dense panicle rice

High grain number is positively correlated with grain yield in rice, but it is compromised because of poor filling of basal spikelets in dense panicle bearing numerous spikelets. The phenomenon that turns the basal spikelets of compact panicle sterile in rice is largely unknown. In order to understand the factor(s) that possibly determines such spikelet sterility in compact panicle cultivars, QTLs and candidate genes were identified for spikelet fertility and associated traits like panicle compactness, and ethylene production that significantly influences the grain filling using recombinant inbred lines developed from a cross between indica rice cultivars, PDK Shriram (compact, high spikelet number) and Heera (lax, low spikelet number). Novel QTLs, qSFP1.1, qSFP3.1, and qSFP6.1 for spikelet fertility percentage; qIGS3.2 and qIGS4.1 for panicle compactness; and qETH1.2, qETH3.1, and qETH4.1 for ethylene production were consistently identified in both kharif seasons of 2017 and 2018. The comparative expression analysis of candidate genes like ERF3, AP2-like ethylene-responsive transcription factor, EREBP, GBSS1, E3 ubiquitin-protein ligase GW2, and LRR receptor-like serine/threonine-protein kinase ERL1 associated with identified QTLs revealed their role in poor grain filling of basal spikelets in a dense panicle. These candidate genes thus could be important for improving grain filling in compact-panicle rice cultivars through biotechnological interventions.

Morphological characterization and evaluation of barnyard millet varieties, cultivars and mutants for varietal identification

The present study was undertaken to characterize barnyard millet (Echinochloa frumentacaea L.) varieties, cultivars and mutants on the basis of morphological descriptors with the objective to identify the key diagnostic characters of the genotypes. A set of 11 barnyard millet genotypes were evaluated in randomized block design with three replications. A total of 12 morphological characters were observed. All the genotypes were classified into different groups based on each character. Among the 12 characters, nine qualitatitive characters viz., pigmentation, inflorescence colour, inflorescence shape, stamen colour, stigma colour, panicle compactness, spikelet arrangement, lower raceme shape, seed colour and three quantitative characters viz., plant height (cm), 50% of flowering (days) and panicle length (cm) were studied. These differences in morphological traits were useful in identification of individual barnyard millet genotypes.

A Large-Scale Genome-Wide Association Analyses of Ethiopian Sorghum Landrace Collection Reveal Loci Associated With Important Traits.

The eastern Africa region, Ethiopia and its surroundings, is considered as the center of origin and diversity for sorghum, and has contributed to global sorghum genetic improvement. The germplasm from this region harbors enormous genetic variation for various traits but little is known regarding the genetic architecture of most traits. Here, 1425 Ethiopian landrace accessions were phenotyped under field conditions for presence or absence of awns, panicle compactness and shape, panicle exsertion, pericarp color, glume cover, plant height and smut resistance under diverse environmental conditions in Ethiopia. In addition, F1 hybrids obtained from a subset of 1341 accessions crossed to an A1 cytoplasmic male sterile line, ATx623, were scored for fertility/sterility reactions. Subsequently, genotyping-by-sequencing generated a total of 879,407 SNPs from which 72,190 robust SNP markers were selected after stringent quality control (QC). Pairwise distance-based hierarchical clustering identified 11 distinct groups. Of the genotypes assigned to either one of the 11 sub-populations, 65% had high ancestry membership coefficient with the likelihood of more than 0.60 and the remaining 35% represented highly admixed accessions. A genome-wide association study (GWAS) identified loci and SNPs associated with aforementioned traits. GWAS based on compressed mixed linear model (CMLM) identified SNPs with significant association (FDR ≤ 0.05) to the different traits studied. The percentage of total phenotypic variation explained with significant SNPs across traits ranged from 2 to 43%. Candidate genes showing significant association with different traits were identified. The sorghum bHLH transcription factor, ABORTED MICROSPORES was identified as a strong candidate gene conditioning male fertility. Notably, sorghum CLAVATA1 receptor like kinase, known for regulation of plant growth, and the ETHYLENE RESPONSIVE TRANSCRIPTION FACTOR gene RAP2-7, known to suppress transition to flowering, were significantly associated with plant height. In addition, the YELLOW SEED1 like MYB transcription factor and TANNIN1 showed strong association with pericarp color validating previous observations. Overall, the genetic architecture of natural variation representing the complex Ethiopian sorghum germplasm was established. The study contributes to the characterization of genes and alleles controlling agronomic traits, and will serve as a source of markers for molecular breeding.

Genomic signatures of adaptation to Sahelian and Soudanian climates in sorghum landraces of Senegal.

Uncovering the genomic basis of climate adaptation in traditional crop varieties can provide insight into plant evolution and facilitate breeding for climate resilience. In the African cereal sorghum (Sorghum bicolor L. [Moench]), the genomic basis of adaptation to the semiarid Sahelian zone versus the subhumid Soudanian zone is largely unknown. To address this issue, we characterized a large panel of 421 georeferenced sorghum landrace accessions from Senegal and adjacent locations at 213,916 single‐nucleotide polymorphisms (SNPs) using genotyping‐by‐sequencing. Seven subpopulations distributed along the north‐south precipitation gradient were identified. Redundancy analysis found that climate variables explained up to 8% of SNP variation, with climate collinear with space explaining most of this variation (6%). Genome scans of nucleotide diversity suggest positive selection on chromosome 2, 4, 5, 7, and 10 in durra sorghums, with successive adaptation during diffusion along the Sahel. Putative selective sweeps were identified, several of which colocalize with stay‐green drought tolerance (Stg) loci, and a priori candidate genes for photoperiodic flowering and inflorescence morphology. Genome‐wide association studies of photoperiod sensitivity and panicle compactness identified 35 and 13 associations that colocalize with a priori candidate genes, respectively. Climate‐associated SNPs colocalize with Stg3a, Stg1, Stg2, and Ma6 and have allelic distribution consistent with adaptation across Sahelian and Soudanian zones. Taken together, the findings suggest an oligogenic basis of adaptation to Sahelian versus Soudanian climates, underpinned by variation in conserved floral regulatory pathways and other systems that are less understood in cereals.

Biochemical and molecular characterisation of exogenous cytokinin application on grain filling in rice

BackgroundPoor filling of grains in the basal spikelets of large size panicles bearing numerous spikelets has been a major limitation in attempts to increase the rice production to feed the world’s increasing population. Considering that biotechnological intervention could play important role in overcoming this limitation, the role of cytokinin in grain filling was investigated based on the information on cell proliferating potential of the hormone and reports of its high accumulation in immature seeds.ResultsA comparative study considering two rice varieties differing in panicle compactness, lax-panicle Upahar and compact-panicle OR-1918, revealed significant difference in grain filling, cytokinin oxidase (CKX) activity and expression, and expression of cell cycle regulators and cytokinin signaling components between the basal and apical spikelets of OR-1918, but not of Upahar. Exogenous application of cytokinin (6-Benzylaminopurine, BAP) to OR-1918 improved grain filling significantly, and this was accompanied by a significant decrease in expression and activity of CKX, particularly in the basal spikelets where the activity of CKX was significantly higher than that in the apical spikelets. Cytokinin application also resulted in significant increase in expression of cell cycle regulators like cyclin dependent kinases and cyclins in the basal spikelets that might be facilitating cell division in the endosperm cells by promoting G1/S phase and G2/M phase transition leading to improvement in grain filling. Expression studies of type-A response regulator (RR) component of cytokinin signaling indicated possible role of OsRR3, OsRR4 and OsRR6 as repressors of CKX expression, much needed for an increased accumulation of CK in cells. Furthermore, the observed effect of BAP might not be solely because of it, but also because of induced synthesis of trans-zeatin (tZ) and N6-(Δ2-isopentenyl)adenine (iP), as reflected from accumulation of tZR (tZ riboside) and iPR (iP riboside), and significantly enhanced expression of an isopentenyl transferase (IPT) isoform.ConclusionThe results suggested that seed-specific overexpression of OsRR4 and OsRR6, and more importantly of IPT9 could be an effective biotechnological intervention towards improving the CK level of the developing caryopses leading to enhanced grain filling in rice cultivars bearing large panicles with numerous spikelets, and thereby increasing their yield potential.

Comparative proteomics of the superior and inferior spikelets at the early grain filling stage in rice cultivars contrast for panicle compactness and ethylene evolution

The breeding programmes in rice aimed at increasing the number of spikelets per panicle have been accompanied by poor grain filling in the inferior spikelets of large panicle rice, leading to yield disadvantage. The present study attempted to understand the reason for differential grain filling in the inferior and superior spikelets by comparative proteomics considering a compact-panicle rice cultivar Mahalaxmi and a lax-panicle rice cultivar Upahar, which show poor and good grain filling, respectively. An initial study of two rice cultivars for panicle compactness and grain filling revealed an inverse correlation between the two parameters. It was further observed that the panicle compactness in Mahalaxmi was associated with a higher evolution of ethylene by the spikelets, both superior and inferior, compared with the lax-panicle Upahar. The proteomic studies revealed that the superior and inferior spikelets of Mahalaxmi differentially expressed 21 proteins that were also expressed in Upahar. However, in Upahar, only two of these proteins were differentially expressed between the superior and inferior spikelets, indicating that the metabolic activities of the spikelets occupying the superior and inferior positions on the panicle were very different in Mahalaxmi compared with those in Upahar. Among the proteins that were downregulated in the inferior spikelets compared with the superior ones in Mahalaxmi were importin-α, elongation factor 1-β and cell division control protein 48, which are essential for cell cycle progression and cell division. Low expression of these proteins might inhibit endosperm cell division in the inferior spikelets, limiting their sink capacity and leading to poor grain filling compared to that in the superior spikelets. The poor grain filling in Mahalaxmi may also be a result of the high evolution of ethylene in the inferior spikelets, which is reflected from the observation that these spikelets showed significantly higher expression of S-adenosylmethionine synthase and the gene encoding the enzyme than the superior spikelets in this cultivar, but not in Upahar; S-adenosynlmethionine synthase catalyses the synthesis of S-adenosylmethionine, the precursor of ethylene biosynthesis.

Assessment of genetic diversity in sorghum using phenotypic markers

Sorghum is an important grain crop in many parts of the world, especially in dry regions. It is an important crop for food and feed, and its role in energy production is currently growing. In Ethiopia, sorghum is a multi-purpose crop used for many different functions such as fuel, housing and animal feed. Information on genetic diversity levels among and within sorghum accessions will increase the efficiency of the sorghum improvement programmes. Field experiments were conducted in Potchefstroom, South Africa, during the summer growing seasons of 2009 and 2010, to estimate the level of phenotypic diversity among 22 sorghum accessions. The experiment was laid out in a randomised complete block design with three replications. Nine qualitative and 20 quantitative morphological traits were recorded. Analysis of variance for the quantitative traits revealed that differences among accessions were highly significant for all traits. Qualitative traits diversity index values varied from 31% (panicle compactness and shape) to 84% (glume colour). The pair-wise genetic distances based on phenotypic traits showed varying genetic distances. Cluster analysis of the phenotypic traits resulted in four distinct groups of accessions with genetic distances ranging from 0.40 to 1.59. Therefore, the phenotypic markers provide a useful measure of genetic distances among sorghum accessions to identify potential donors or parental material for future breeding efforts.

Patterns of morphological variation of sorghum (Sorghum bicolor (L.) Moench) landraces in qualitative characters in North Shewa and South Welo, Ethiopia

Thirty-four sorghum (S. bicolor (L.) Moench) landraces consisting of 1020 individual plants (30 plants of each landrace) collected from five agroecological sites (ecosites) in North Shewa and South Welo regions of Ethiopia (Bati 8, Fontenina 5, Haik 2, Layignaw ataye 17 and Merewa Adere 2) were classified on the basis of 4 classifying variables: administrational zones; Woredas (smallest administrative unit), ecosite of origin and altitude. Morphological variation for the fourteen qualitative characters that showed two or more phenotypic classes were estimated using the Shanon–Weaver diversity index (H′). Phenotypic variation was found between and within each classifying variables. The value of H′ for all landraces varied from 0.32 to 0.98 with an overall mean of 0.77±0.04. One-way analysis of variance (ANOVA) showed significant differences between characters within all classifying variables and this contributed to the largest portion of the total variance. Cluster analysis based on ordinal variables grouped the landraces into five clusters. A higher proportion of landraces sharing similar altitude classes and similar ecosites were grouped together. Panicle compactness and shape as well as stalk juiciness were the predominant characters in grouping the landraces into their respective clusters. Panicle compactness and shape also contributed relatively more to altitudinal and ecological differentiation. This differential distribution of landraces with panicle types with respect to compactness and shape revealed the adaptive significance of panicle compactness and shape that reflected the patterns of distribution of different races in north Shewa and south Welo. χ2 test of all characters did not show significant differences between the frequencies of observed and expected characters.

Quantitative trait loci for grain quality, productivity, morphological and agronomical traits in sorghum (Sorghum bicolor L. Moench)

Quantitative trait loci (QTLs) for grain quality, yield components and other traits were investigated in two Sorghum caudatum×guinea recombinant inbred line (RIL) populations. A total of 16 traits were evaluated (plant height, panicle length, panicle compactness, number of kernels/panicle, thousand-kernel weight, kernel weight/panicle, threshing percentage, dehulling yield, kernel flouriness, kernel friability, kernel hardness, amylose content, protein content, lipid content, germination rate and molds during germination and after harvest) and related to two 113- and 100-point base genetic maps using simple (SIM) and composite (CIM) interval mapping. The number, effects and relative position of QTLs detected in both populations were generally in agreement with the distributions, heritabilities and correlations among traits. Several chromosomal segments markedly affected multiple traits and were suspected of harbouring major genes. The positions of these QTLs are discussed in relation to previously reported studies on sorghum and other grasses. Many QTLs, depending on their relative effects and position, could be used as targets for marker-assisted selection and provide an opportunity for accelerating breeding programmes.

Sources and mechanisms of resistance to sorghum head bug, Eurystylus immaculatus Odh. in West Africa

Sorghum is one of the most important cereal crops in West Africa, and the head bug, Eurystylus immaculatus Odh. (Hemiptera: Miridae) is the key pest of grain sorghum in this region. A range of sorghum genotypes were evaluated for resistance to sorghum head bug at Sotuba (Mali) and Kamboinse (Burkina Faso). Genotypes CSM 388, IS 14332, Malisor 84-7, Sakoika. S 29 and Kamboinse local were resistant to head bugs. both under natural and headcage screening. Head bug resistant genotypes had a lower percentage of head bug damaged grain. The food quality of head bug damaged grain was very poor and unacceptable. Cultivar non-preference was identified as a component of resistance to head bugs. and CSM 388 was nonpreferred compared to E 35-1. Panicle compactness was positively associated with head bug numbers and grain damage. However, genotypes with loose panicles were also susceptible to bugs. Long glumes (>5 mm), days to glume opening (>20 days after anthesis), >50% covering of the grain by the glumes, and grain hardness contribute towards resistance to Eurystylus immaculatus. This information will be useful for developing a programme to breed for resistance to this insect in West Africa.

Influence of panicle compactness and host plant resistance in sequential plantings on population increase of panicle‐feeding insects inSorghum bicolor(L.) Moench

The effects of panicle compactness and host plant resistance on the rate of population increase of sorghum midge (Contarinia sorghicola Coq.), head bugs (Calocoris angustatus Leth.) and head caterpillar (Helicoverpa armigera Hb.) in large concentric plots over three sequential sowings during the 1985–86 rainy seasons were studied. Early‐planted crops suffered less damage than the late‐planted crops. H. armigera damage was negligible in genotypes with loose panicles. Calocoris angustatus population increase was lower in genotypes with loose panicles. Panicle compactness did not affect the damage caused by C. sorghicola and Campylomma spp. Host plant resistance had a marked effect on the rate of population increase across sowing dates in the case of sorghum midge and head bugs. Thus, cultivars with resistance to insects and/or with loose panicles can help to reduce the losses caused by panicle‐feeding insects in sorghum.

Partial Life Tables for Corn Earworm (Lepidoptera: Noctuidae) on Compact- and Loose-Panicle Sorghum Hybrids

Population dynamics were assessed and partial life tables constructed for corn earworm, Helicoverpa zea (Boddie), infesting panicles of two sorghum, Sorghum bicolor (L.) Moench, hybrids in field experiments in central Texas in 1985 and 1986. The hybrids were commercially acceptable types, similar agronomically and developmentally but differing in degree of panicle compactness at maturity. Almost all oviposition on panicles occurred just before and during flowering. Subsequent larval stages were associated with progressive stages of panicle development. Significantly more corn earworm eggs and larvae were recovered from panicles of the compact-panicle hybrid than the loose-panicle hybrid. However, life table construction revealed that the distribution and level of egg and larval mortality were similar for corn earworm on either panicle type. Data from all experiments revealed that real mortality ( rx ) was >98% by the end of the last larval stage, and was >90% during the egg and small larval stages. Parasitism by Trichogramma spp. and failure to hatch caused the greatest amount of egg mortality. Few parasitized larvae were found. Disease-induced larval mortality was low but was highest among large larvae. The greater number of larvae recovered from sorghum with compact panicles than those with loose panicles was a function of the greater number of eggs deposited on those panicles. Significant relationships existed between abundance of large larvae (>24 mm) and that of small and medium larvae. Equations were derived to predict densities of large corn earworm larvae on sorghum panicles based upon densities of earlier corn earworm life stages.

EVALUATION OF SURVEY METHODS FOR ESTIMATING SORGHUM MIDGE (DIPTERA: CECIDOMYIIDAE) DENSITIES IN GRAIN SORGHUM

Six methods for sampling field populations of ovipositing sorghum midge, Contarinia sorghicola, in grain sorghum panicles were compared to an absolute sampling method. The methods evaluated were the visual, tap, remove, shake, beat-bucket, and grab. Population estimates obtained by visual examination were similar to absolute estimates when population density was low but significantly differed at mean midge densities above 9.2/panicle. The remaining sampling method density estimates were significantly less than the absolute method estimates. The visual examination method was relatively time efficient taking ca. one minute per panicle to complete. The effect of panicle compactness (open, medium, and compact) on the precision of the visual examination was investigated. Accuracy of the visual examination method significantly decreased as panicle compactness increased. This may be a result of either obstructed vision or increased density of midges with compactness or a combination of both.

Quantitative Inheritance and Correlations of Agronomic and Grain Quality Traits of Sorghum1

Two S2 or S1‐derived families from each of 118 S0 plants from Purdue random‐mated population (PP18) of Sorghum bicolor (L.) Moench, were evaluated in a randomized complete‐block design over 1 or 2 years. Genetic parameters were estimated for days to bloom, plant height, lodging, panicle compactness, panicle weight, kernel weight, weathering, hardness, and vitreosity to assess breeding potential of the population. Additive variances were estimated using a weighted least‐squares procedure. Additive variances were significant for all traits. The additive genetic coefficients of variation ranged from 2.9% for days to bloom to 25.5% for lodging. Narrow‐sense heritabilities ranged from 0.349 to 0.734 for S0‐derived family selection (unit equals mean of S2 progeny of two S1/S0 plants in two replicatio/ts in either 1 or 2 years). Heritabilities ranged from 0.359 to 0.842 for S1‐derived family selection (unit equals mean of S2 progeny of a single S1/S0 plant in two replications in either 1 or 2 years). Additive genetic (−0.737 to 0.839) and phenotypic (−0.649 to 0.710) correlations were high among agronomic traits and among quality traits, and low between agronomic and quality traits. Kernel hardness had strong correlations with weathering (negative) and vitreosity (positive). Direct selection responses (percentage of mean) ranged from 3.70 to 28.58% and from 5.10 to 37.10% for S0‐ and S1‐derived family selection, respectively, Correlated responses were lower than direct responses for most traits. However, for some pairs of traits the difference between the two responses was not large. The results suggested good potential for conventional breeding methods and early generation selection for all traits tested. More improvement would be expected from S1‐derived than from S0‐derived family selection.