Male-sterile Sorghum Research Articles

PSIV-20 The Effect of Silage Additives on Male Sterile Sorghum Fermentation Heat Production and Feed-Out Stability

Abstract The objective was to compare the effect of applying silage additives to male sterile sorghum hybrids on temperature production during ensiling time (30 d) and at feed-out period after 30 or 90 d of ensiling period. Two male-sterile sorghum hybrids; F430 and F465, with and without BMR12 trait, respectively (Richardson Seed Ltd.); were randomly allocated in plots blocked by irrigation section in a dairy farm in West Texas. During harvest, duplicate samples from each plot were obtained, placed on plastic trays, and transported to one of three stations to be treated with chemical silage preservative (SG, SiloGuard), heterofermentative bacteria inoculant with mold inhibitor solution (SM, Silage Maker 250) or distilled water (DW, control). Treatments were applied with spray bottles following a protocol that consisted of two sets of 5 sprays (1.1 mL each and 11 mL total) followed by mixing of the forage. Personnel applying the treatment were blind as to which treatment they were applying and all spray bottles, trays and tables from each station were color coded to prevent cross contamination. After treated, 3.63 kg of forage was packed in three consecutive steps using a manual press on 4.7L buckets (Uline) and a temperature data logger was placed in the center of each of the 30 d mini silos. The amount of material packed was estimated to achieve a 230 kg of DM/m3 compaction at 30% DM of the forage. At opening, the material from each silo was moved to a tray and mixed to be homogenized and exposed to oxygen. Then, the material was added back to its correspondent bucket until it filled up to the border without compressing. Heat production during the feed-out period and air-stability were assessed for both ensiling periods, whereas fermentation heat production during ensiling period was only assessed for 30 d silos. Statistical analysis was performed using mixed linear regression models (GLIMMIX procedure of SAS) with ensiling period, hybrid, treatment and the interaction of day and treatment included in the model as independent variables. Fourth root and natural log transformation were performed to obtain a normal distribution of residuals, back transformed LSM and 95% CI are reported in Table 1. Treatment effected the silage temperature during the feed-out period (P < 0.0001) and air-stability test (P = 0.02). Whereas a tendency was observed for daily heat production during the ensiled period (P = 0.07). Male-sterile sorghum silage treated with SG had the least temperature during the ensiling period and longer air-stability than SM.

PSIV-21 Comparing the Nutritional Value and the Trade-Off Between Sugars and Starch of Male-Sterile with Non-Sterile Sorghum Hybrids

Abstract The objective of this study was to assess the effect male-sterile versus non-sterile sorghum hybrids on nutritional value with emphasis on carbohydrates. The experiment was conducted on a dairy farm in West Texas under center pivot irrigation. Two male-sterile (Non-BMR, F465; and BMR12, F430) and three non-sterile sorghum hybrids (non-BMR F10; BMR12, F382, and F431; Richardson Seeds) were used in a split-plot design to reduce cross-pollination. Because of westerly prevailing winds, male-sterile hybrids were allocated to the west and non-sterile hybrids to the east, plots were blocked by irrigation section, and replicated 3 times. Plots were harvested 148 days after seeding with non-sterile hybrids after the hard dough stage and male-sterile hybrids 7 weeks after boot stage and harvested with a self-propelled forage harvester with a theoretical length of cut of 12 mm and roll gap setting at 2 mm. Duplicate samples of freshly chopped forage were obtained from each plot and immediately placed into a cooler with ice until harvest was completed. Samples were then frozen until shipped to Rock River laboratory where near-infrared spectroscopy analysis was performed. In addition, water soluble carbohydrates (WSC) and NDFD at 30h were analyzed with wet chemistry methods. The statistical analysis was performed using mixed linear regression models (GLIMMIX procedure of SAS). Type (Sterile and non-Sterile), trait (BMR12 and non-BMR) and its interaction were included as predictor variables in all models. Normal distribution of residuals was assessed using Shapiro-Wilk test (P > 0.05) and visual diagnostic of residual plots. A summary of the results is presented in Table 1. WSC was 2.5-fold greater for the sterile hybrids when compared with non-sterile, whereas starch was 2.2-fold greater for non-sterile when compared with sterile hybrids (P < 0.0001). Non-fiber carbohydrates were greater for non-sterile over sterile sorghum hybrids (P < 0.0001); however, non-sterile hybrids were past the optimal stage of harvest (soft dough), which would result in poor digestibility of grain starch and protein. In addition, crude protein (CP) was less for sterile than non-sterile (8.29% and 10.2% respectively; P < 0.0001). Compared with non-sterile hybrids, male sterile hybrids DM was decreased (28.4% and 40.8%, respectively; P < 0.0001) due to its proportionally greater vegetative plant parts compared with reproductive plant parts. The trade-off between WSC and starch in male-sterile sorghum hybrids is because sugars are not translocated to the grain where starch is developed as in non-sterile hybrids. This research indicates that concerns about low sorghum starch digestibility can be overcome by using male-sterile sorghum hybrids that will, at least partially, compensate for the reduced starch yield by increasing water-soluble carbohydrates storage.

Estimating reliability for evaluating nitrate accumulation in sorghum (Sorghum bicolor L. Moench) inbred A‐lines

AbstractSorghum is an important forage crop in many cropping systems. Nitrate can accumulate in the vegetative plant tissue to levels high enough that result in fatality when fed to ruminant livestock when grown under high nitrate conditions. If variation among inbred lines can be documented for nitrate concentration, it may be possible to reduce nitrate accumulation within forage sorghum hybrids by selecting inbred lines having lower nitrate accumulation. The goal of this study was to evaluate a diverse set of male‐sterile sorghum inbred lines grown under high nitrate conditions, to observe if genotypic variation exists among lines used to produce forage sorghum hybrids. Forty replicates of 20 sorghum A‐lines were grown in a greenhouse and received either 272 kg ha−1 or 408 kg ha−1 of actual nitrogen per plant through applications of ammonium nitrate. Variance components were extracted from linear regression models and reliability was estimated on an entry‐mean basis. Leaf and stem reliability estimates were 0.95 and 0.93, respectively. These reliability estimates indicate the genetic variance comprised most of the phenotypic variance, and that our measurements were consistent. Significant differences were also observed between genotypes for both leaf and stem tissue. Therefore, sufficient genetic variance exists for developing male sterile sorghum inbred lines having leaf nitrate concentrations below the potentially lethal toxicity threshold of 10,000 μg g−1.

Development of InDels markers for the identification of cytoplasmic male sterility in Sorghum by complete chloroplast genome sequences analysis.

Cytoplasmic male sterility (CMS) is predominantly used for F1 hybrid breeding and seed production in Sorghum. DNA markers to distinguish between normal fertile (CMS-N) and sterile (CMS-S) male cytoplasm can facilitate F1 hybrid cultivar development in Sorghum breeding programs. In this study, the complete chloroplast (cp) genome sequences of CMS-S and Korean Sorghum cultivars were obtained using next-generation sequencing. The de novo assembled genome size of ATx623, the CMS-S line of the chloroplast, was 140,644bp. When compared to the CMS-S and CMS-N cp genomes, 19 single nucleotide polymorphisms (SNPs) and 142 insertions and deletions (InDels) were identified, which can be used for marker development for breeding, population genetics, and evolution studies. Two InDel markers with sizes greater than 20 bp were developed to distinguish cytotypes based on the copy number variation of lengths as 28 and 22 bp tandem repeats, respectively. Using the newly developed InDel markers with five pairs of CMS-S and their near isogenic maintainer line, we were able to easily identify their respective cytotypes. The InDel markers were further examined and applied to 1,104 plants from six Korean Sorghum cultivars to identify variant cytotypes. Additionally, the phylogenetic analysis of seven Sorghum species with complete cp genome sequences, including wild species, indicated that CMS-S and CMS-N contained Milo and Kafir cytotypes that might be hybridized from S. propinquum and S. sudanese, respectively. This study can facilitate F1 hybrid cultivar development by providing breeders with reliable tools for marker-assisted selection to breed desirable Sorghum varieties.

Evaluation of A3 cytoplasmic male sterile forage sorghum lines for resistance to sugarcane aphid.

Three known sugarcane aphid-resistant pollinator parents were sterilized in A3 cytoplasmic male sterility and were confirmed in this study to be resistant to sugarcane aphid allowing for the development of sugarcane aphid-resistant forage hybrids. We utilized A3 cytoplasmic male sterility and converted known sugarcane aphid-resistant sorghum TX 2783, and newly released R. LBK1 (Reg. No. GP-865, PI 687244) and R. LBK2 (Reg. No. GP-866, PI 687245) into A3 sterility to determine if the sterile counterparts would also equally express tolerance and or antibiosis to sugarcane aphid. Free-choice flat screen trials and life-table demographic studies were utilized and compared to know susceptible/fertile entries KS 585, and TX 7000, and known resistant/fertile entries TX 2783 and DKS 37-07. The R. LBK1 fertile entry was more tolerant than the known susceptible entries KS 585 and TX 7000, but was not as resistant as the other resistant entries, sustaining a damage rating of 6.0 across two different screen trials. The sterile A3 R. LBK2 showed a greater tolerance and expressed higher levels of antibiosis during aphid reproductive studies when compared to the known resistant and fertile TX 2783. All other fertile (R. LBK2, TX2783) and the A3 male sterile counterparts (A3 R. LBK2, A3 TX2783) were very similar in expression of high levels of tolerance and exhibited statistically similar damage ratings of 3.3-4.3 when exposed to sugarcane aphids. No entry, either fertile or sterile, was as tolerant as DKS 37-07, a known resistant commercial hybrid. Other plant measurements including percent loss in chlorophyll content, difference in plant height, and number of true leaves for sugarcane aphid infested versus non-infested were very consistent and highly correlated with damage ratings. Antibiosis was also exhibited in both fertile and sterile versions of the resistant lines. There was a 2 × reduction in fecundity between the R. LBK1 fertile and its sterile A3 R. LBK1 when compared to the susceptible KS 585 and TX 7000; however, the remaining fertile and sterile entries had 3.8 × to 5.8 × decrease in fecundity when compared to the susceptible KS 585 and TX 7000. Other measurements in life-table statistics such as nymphs produced/female/d, and the intrinsic rates of increased were significantly lower for all fertile and sterile lines, showing that antibiosis significantly affected sugarcane aphid reproduction. In conclusion, the A3 cytoplasmic male sterility shows consistency for maintaining the single dominant trait SCA-resistant trait of TX 2783 for expressing both antibiosis and tolerance, and great utility in the development of sugarcane aphid-resistant forage sorghums.

Comparative analysis of the efficacy of selected gametocide agents in sorghum (Sorghum bicolor [L.] Moench)

A new generation of chemical hybridization agents (CHAs) or gametocides has shown potential to induce male sterility in predominantly self-fertilizing crops, including sorghum (Sorghum bicolor [L.] Moench). There is a lack of information on the relative efficacy of the various available CHAs for large-scale application in plant breeding programs. Therefore, the objective of the present study was to compare the relative effectiveness of three selected CHAs to induce male sterility in sorghum under a controlled environment for hybridization. Foliar applications of three CHAs and a control (ethrel, trifluoromethanesulfonamide [TFMSA], ethyl 4-fluorooxanilate [E4FO] and distilled water [control]) were tested using three grain sorghum genotypes (ICS-1, ICS-2 and ICS-3) in two seasons. The 24 treatment combinations consisting of 4 levels of CHAs, 3 sorghum varieties and two seasons were laid out using a randomized complete block design with three replications. Data on pollen sterility, pollen diameter, plant height, and panicle height were collected and analyzed. Results showed that the CHAs had significant (p<0.05) differences for efficacy of inducing male sterility in sorghum. Ethrel at a dose of 1 gl-1 induced the highest pollen sterility (98% in both seasons) but was highly phytotoxic with at least 60% mortality in the test population in both seasons, making it unsuitable for practical application. TFMSA (2 mg per plant) and E4FO (1 gl-1) d induced 93% male sterility with minimal phytotoxic effects (20 to 30%). Application of either TFMSA at 2mg per plant after flag leaf emergence or 1gl-1 of E4FO at panicle initiation can be used to successfully induce male sterility in sorghum under greenhouse conditions

Sorghum bicolor x S. halepense interspecific hybridization is influenced by the frequency of 2n gametes in S. bicolor

Tetraploid johnsongrass [Sorghum halepense (L.) Pers.] is a sexually-compatible weedy relative of diploid sorghum [Sorghum bicolor (L.) Moench]. To determine the extent of interspecific hybridization between male sterile grain sorghum and johnsongrass and the ploidy of their progeny, cytoplasmic (CMS), genetic (GMS) and chemically induced male sterile lines of Tx623 and Tx631 were pollinated with johnsongrass pollen. At maturity 1% and 0.07% of the developing seeds of Tx623 and Tx631 respectively were recovered. Ninety-one percent of recovered hybrids were tetraploid and two percent were triploid, the tetraploids resulting from 2n gametes present in the sorghum female parent. Their formation appears to be genotype dependent as more tetraploids were recovered from Tx623 than Tx631. Because a tetraploid sorghum x johnsongrass hybrid has a balanced genome, they are male and female fertile providing opportunities for gene flow between the two species. Given the differences in 2n gamete formation among Tx623 and Tx631, seed parent selection may be one way of reducing the likelihood of gene flow. These studies were conducted in controlled and optimum conditions; the actual outcrossing rate in natural conditions is expected to be much lower. More studies are needed to assess the rates of hybridization, fitness, and fertility of the progeny under field conditions.

Identification of the First Nuclear Male Sterility Gene (Male‐sterile 9) in Sorghum

The male-sterile 9 (ms9) is a novel nuclear male-sterile mutant in sorghum. The Ms9 gene encodes a PHD-finger transcription factor critical for pollen development. The identification of the Ms9 gene provides a strategy to control male sterility in sorghum. Nuclear male sterility (NMS) is important for understanding microspore development and could facilitate the development of new strategies to control male sterility. Several NMS lines and mutants have been reported in sorghum [Sorghum bicolor (L.) Moench] previously. However, no male-sterile gene has been identified, hampering the utility of NMS in sorghum breeding. In this study, we characterized a new NMS mutant, male sterile 9 (ms9), which is distinct from all other reported NMS loci. The ms9 mutant is stable under a variety of environmental conditions. Homozygous ms9 plants produced normal ovaries but small pale-colored anthers that contained no pollen grains. Microscopic analyses revealed abnormal microspore development of ms9 at the midmicrospore stage, causing degeneration of microspore inside the anther lobes and male sterility of ms9 plants. Using MutMap, we identified the Ms9 gene as a plant homeotic domain (PHD)-finger transcription factor similar to Ms1 in Arabidopsis thaliana (L.) Heynh. and Ptc1 in rice (Oryza sativa L.). Ms9 is the first NMS gene identified in sorghum. Thus, the Ms9 gene and ms9 mutant provide new genetic tools for studying pollen development and controlling male sterility in sorghum.

Registration of BTx623ms8, a New and Easily Identifiable Nuclear Male Sterile Mutant in Sorghum

The USDA–ARS has released a new nuclear male sterile sorghum [Sorghum bicolor (L.) Moench] mutant BTx623ms8 (Reg. No. GS‐786, PI 682727). Previously, seven sorghum nuclear male sterile mutants have been reported, but three are no longer available. Here we register a new nuclear male sterile mutant isolated from a mutagenized BTx623 mutant library that is genetically different from any of the four male sterile mutants currently available. The ms8 mutant had microscopic transparent anthers that abort early during microsporogenesis. It can be easily identified at early stages of anthesis by the appearance of prominent white, hairy stigma, rather than yellow anthers as seen in BTx623 and all other fertile sorghum accessions. We have developed BC6F2 seeds that produce approximately 50% male sterile plants by pollinating the homozygous ms8 mutants with the heterozygous fertile plants. The ms8 is a single recessive nuclear gene mutation and can be easily bred into other sorghum lines through recurrent backcrossing, broadening the utility of this easily recognizable nuclear male sterility.

Evaluation of effective gametocides for selective induction of male sterility in sorghum

Effective gametocides can serve as alternative agents to induce male sterility in sorghum. The objectives of this study were to evaluate the effectiveness of selected male gametocides in sorghum, to determine the optimum concentration of the chemicals and to investigate its possible effect on female sterility. Ethyl 4-fluorooxanilate (E4FO) and ethrel were evaluated on three genotypes of sorghum. The gametocides were sprayed at five concentrations at the booting stage when the panicles were released halfway from the flag leaf. Pollen and spikelet sterility were assessed using light and scanning electron microscopes. Both chemicals were effective in inducing male sterility in sorghum. However, E4FO was the more potent chemical, inducing complete male sterility with high female fertility and relatively less phytotoxicity at lower concentrations, while higher concentrations of ethrel were required to give complete male sterility. E4FO induced on average of 99.5% male sterility at 2 mg/l in all the varieties, while with ethrel 97% male sterility was obtained at 3 ml/l. Therefore we recommend to use E4FO at 2 mg/l and ethrel at 3 ml/l as male sterilizing agents to facilitate controlled crosses in sorghum.

Inheritance of reversions to male fertility in male-sterile sorghum hybrids with 9E male-sterile cytoplasm induced by environmental conditions

Heritable phenotypic alterations occurring during plant ontogenesis under the influence of environmental factors are among the most intriguing genetic phenomena. It was found that male-sterile sorghum hybrids in the 9E cytoplasm from the F1 and F2 generations, which were obtained by crossing CMS lines with different fertile lines grown in field conditions, when they have been transferred to greenhouse produce fertile tillers. Lines created by the self-pollination of revertant tillers exhibit complete male fertility upon cultivation under various environments (in the field, “dry plot,” “irrigated plot”). In a number of test-crosses of revertants to CMS lines in the 9E cytoplasm, restoration of male fertility in F1 hybrids was found, indicating that revertants possess functional fertility-restoring genes. A high positive correlation was found between the fertility level of the test-cross hybrids and the hydrothermal coefficient (the ratio of the sum of precipitation to the sum of temperatures) during the booting stage and pollen maturation (r = 0.75…0.91; P < 0.01), suggesting that a high level of plant water availability is needed for the expression of fertility-restoring genes of revertants. These data show that the fertility-restoring genes for the 9E cytoplasm are dominant in conditions of high water availability and recessive in drought conditions; reversions to male fertility are due to up-regulation of fertility-restoring genes by a high level of water availability. Comparative MSAP-analysis of DNA of malesterile and male-fertile test-cross hybrids using HpaII/MspI restrictases and primers to polygalacturonase gene ADPG2, which is required for cell separation during reproductive development, and gene MYB46, the transcription factor regulating secondary wall biosynthesis, revealed differences in the number and the length of amplified fragments. Changes in the methylation of these genes in conditions of drought stress are apparently the reason for male sterility of sorghum hybrids in the 9E cytoplasm. These data demonstrate that methylation of nuclear genes in sterility-inducing cytoplasm may be one of mechanisms causing the CMS phenomenon.

Floral traits, ergot resistance and grain yield relationships in infected male-sterile sorghum A-lines

1 INIFAP-Campo Experimental Rio Bravo, Km 61 Carretera Reynosa-Matamoros, Apdo. Postal 172, 88900, Rio Bravo, Tamaulipas, Mexico Departments of Seed Production, Genetics, Phytopathology, and Botany, Colegio de Postgraduados, Campus Montecillo, Km. 36.5 Carretera Mexico-Texcoco, 56230, Montecillo, Estado de Mexico (E-mail: leopoldo@colpos.mx) 5 INIFAP-Campo Experimental Bajio, Km. 65 Carretera Celaya-San Miguel Allende, Apdo. Postal 112, 38810, Celaya, Guanajuato, Mexico

Incidence and severity of ergot (Claviceps africana Frederickson, Mantle and de Milliano) in two male-sterile sorghum lines as a function of distance from pollen source and its impact on seed production and quality

Incidence and severity of ergot (Claviceps africana Frederickson, Mantle and de Milliano) in two male-sterile sorghum lines as a function of distance from pollen source and its impact on seed production and quality

Cultural characteristics, morphology, and variation within Claviceps africana and C. sorghi from India

Sorghum ergot in India is caused by Claviceps africana and C. sorghi. The distributions of these two species in India is not known. Eighty-nine sorghum ergot isolates were cultured from young sphacelia obtained from male sterile sorghum plants artificially inoculated using inoculum collected in the field. Based on cultural characteristics, the isolates were separated into two groups which differed distinctly in the morphology of their sphacelia, conidia, and sclerotia. Marked differences also were observed in rates of secondary conidial production and disease spread between the groups. In combination with molecular evidence, our results confirm that the isolates placed in Group I represent C. africana and Group II isolates represent C. sorghi. C. africana was found to be widely distributed in all sorghum growing areas of India. The species first described as occuring in India, C. sorghi, appears to be restricted to a few locations in the states of Maharashtra, Andhra Pradesh, and Karnataka.

Dominant male sterility in sorghum: effect of nuclear background on inheritance of tissue-culture-induced mutation

Occurrence of genetic instability and formation of stable mutations are basic genetic processes. This study demonstrates that nuclear background may influence the formation of stable dominant nuclear gene of male sterility (MS) on the basis of unstable mutation, which was induced in tissue culture of the sorghum haploid (cv. Milo-145). The mutants with complete or partial MS segregated in variable ratios in the progenies of diploid regenerants were obtained from different experiments on cultivation of haploid tissues. In the Milo-145 genetic background the mutation demonstrated somatic instability and was gradually eliminated by self-pollination of partially sterile plants. Hybridization of the MS-plants with the sorghum line SK-723, a fertility-restorer of the cytoplasmic MS A1 (milo) type, maintained the induced mutation. By repeated backcrossing of MS-plants with SK-723, the male-sterile versions of this line (SK-723- Ms(tc)) have been created. In BC-generations, fertile, partially and completely sterile plants were observed. The MS-plants from BC-generations are proposed to contain a dominant gene Ms(tc) while fertile plants were ms(tc)/ms(tc) homozygotes. Crossing the original MS-plants with SK-723 was a key factor in stabilization of the Ms(tc) gene. Dominant expression of the Ms(tc) was observed in male-sterile versions of other sorghum lines created by backcrossing to SK-723- Ms(tc). The lines fertility-restorers for this mutation have been revealed. In the crosses of restored F1 hybrids with emasculated plants of the non-restoring line, the Ms(tc) has been transferred through the pollen and manifested in the F1 generation. The possibility of the Ms(tc) originating as a result of interaction of an unstable allele of the Milo-145 with the SK-723 genome is discussed.

A Diploid, Interspecific, Fertile Hybrid from Cultivated Sorghum, Sorghum Bicolor, and the Common Johnsongrass Weed Sorghum Halepense

Valuable agronomic traits are often present but inaccessible in the wild relatives of cultivated crop species. Utilization of wild germplasm depends on the production of fertile interspecific hybrids. Several unsuccessful attempts have been made to hybridize cultivated sorghum with its wild relatives to broaden its genetic base and enhance agronomic value. The successful approach used in this study employed the nuclear male sterility gene ms3 to generate a diploid fertile hybrid between the diploid cultivated sorghum (Sorghum bicolor (L) Pers.) and its weedy tetraploid wild relative Johnsongrass (Sorghum halepense (L.) Pers.). Eight sorghum plants were selected from a Nebraska stiff stalk collection that contains the male sterility gene ms3 and were used as the female parent. About 36,000 florets of male sterile sorghum were pollinated with Johnsongrass pollen to produce an average of one well-developed and 180 severely shriveled seed/18,000 crosses. The well-developed seed gave rise to a self-fertile diploid, while none of the shriveled seed were able to germinate. The F1 hybrid was confirmed by using cultivated sorghum SSR markers and was selfed to produce an F2 population. A sub-sample of 96 segregating F2 plants was examined with 36 sorghum polymorphic SSR markers. Thirty-four markers showed a normal 1:2:1 segregation ratio, evidence of normal recombination across the genome. Preliminary results showed that several desirable traits from Johnsongrass, including resistance to greenbug and chinch bug and adaptability to cold temperatures, were expressed in the resulting progenies. These observations suggest that speciation within the genus Sorghum, giving rise to widely divergent phenotypes, is effected largely by ploidy-maintained crossing barriers but apparently not by extensive genomic divergence.

Survival of Claviceps africana Within Sorghum Panicles at Several Texas Locations.

Survival of the sorghum ergot fungus, Claviceps africana, based on pathogenicity of recovered macroconidia used to inoculate sorghum (Sorghum bicolor), was measured in 2000 over the course of the year at five locations in Texas representing three climates. The experiment was repeated in 2001. Sphacelia associated with infected sorghum panicles were placed in nylon mesh bags and either buried at a 10-cm depth, placed on the soil surface, or suspended 61 cm above the ground. Samples were recovered after 4, 8, and 12 months and assessed for pathogenicity of surviving macroconidia by macerating tissue in water and spraying it onto panicles of flowering male-sterile sorghum in the greenhouse. Survival of ergot macroconidia in recovered panicles declined at all locations after the first 4 months that panicles were left in the field. The decline in viability during this period was greater in 2001 than in 2000. In 2000, survival after 4 months was greatest at Lubbock and Bushland, which have a continental steppe climate, than at the other three Texas locations, Weslaco and Corpus Christi, which have a subtropical subhumid climate, and College Station, which has a subtropical humid climate. However, this difference in survival was not as pronounced in 2001. Additionally, after 8 months, survival levels at all locations were similar. At the end of 12 months, infective macroconidia were found only at Lubbock in 2000, and only at Lubbock and College Station in 2001. Ergot macroconidia can survive in all major sorghum production areas of Texas; thus, conidia would not need to move long distances in order to initiate an epiphytotic.

Transcript profiling of male-fertile and male-sterile sorghum indicates extensive alterations in gene expression during microgametogenesis

Male-sterile sorghum carrying the IS1112C cytoplasm represents an unusual example of aberrant microgametogenesis wherein microspores develop into inviable pollen that remain physically intact until anther exsertion. These inviable pollen grains do not deposit starch, yet fluoresce with the vital stain fluoroscein diacetate. We sought to elucidate the extent of differential gene expression in this subtle example of defective microgametogenesis through cDNA-AFLP transcript profiling of near-isogenic male-fertile and male-sterile plants at an early stage representing early-mid microspores to early pollen, 7–11 days prior to anthesis, and a late stage representing young to nearly mature pollen, spanning the terminal 96 h of pollen development. The transition from early to late stages is characterized by changes in abundance of nearly 33% of shared transcripts, and early- or late-specific expression of about 10% of transcripts. Male-sterile plants exhibit extensive changes in regulatory patterns characteristic of fertile plants, including premature expression of late-specific, and prolonged expression of early-specific, transcripts. Genome-wide transcriptome patterns indicate the expression of an estimated 12,000 genes in early-mid microspores, and the abundance of at least 15% of these transcripts is altered in male-sterile plants. A near-isogenic line restored to male fertility is characterized by apparent normalized expression of most of these transcripts. The development of the microgametophyte is thus characterized by dynamic programmed changes in gene expression, and the expression of male sterility compounds these changes in a complex manner.

Cytological investigation of male sterility in sorghum caused by a dominant mutation (Ms tc ) derived from tissue culture

Male sterility mutations are an important tool in the investigation of anther and pollen development and for obtaining hybrid seeds in plant breeding. Cytological analysis of microsporo- and microgameto-genesis in sorghum plants with dominant mutation of male sterility (Ms tc ) derived from tissue culture has been carried out. Using substitution backcrosses, this mutation was introduced first into the nuclear background of the fertile sorghum line SK-723 and from this line into Volzhskoe-4w (V-4w). The mechanism of Ms tc action on anther and pollen development differed in different nuclear backgrounds. In SK-723, phenotypic expression of Ms tc began before the beginning of meiosis, which resulted in degeneration of sporogenous tissue in some anthers and in significant disturbances of anther morphology. In microsporocytes that did not degenerate, the frequency of non-specific meiotic abnormalities characteristic of the fertile line SK-723 significantly increased. In addition, in the mutant plants, a number of specific meiotic abnormalities—almost complete desynapsis, and formation of syncytial structures—were observed, apparently the consequence of Ms tc action. In mono- or bi-nucleate microspores, degenerative processes resulting in formation of empty or anomalously coloured pollen grains led to almost complete male sterility. In the V-4w nuclear background, changes in anther structure and meiotic disturbances were infrequent. The degenerative processes began at the uni- or binucleate microspore stage and resulted in formation of empty or abnormally coloured pollen grains, and in partial pollen sterility. Thus, the same nuclear male sterility-inducing mutation in different nuclear backgrounds affects different stages of pollen development.

Transmission of Claviceps africana Spores from Diseased to Non-Infected Sorghum by Corn Earworm Moths, Helicoverpa zea

ABSTRACT The potential of corn earworm moths Helicoverpa zea, an important pest of sorghum in Texas, as a passive vector of sorghum ergot, Claviceps africana was assessed. Laboratory-reared (females and males) and field-moths trapped in sex pheromone traps were confined in screen cages with potted male-sterile sorghum line AT×623 that had been artificially infected with sorghum ergot and was producing massive amounts of honeydew that contained spores of the fungus. In the cages, moths were observed feeding on the honeydew. When laboratory-reared moths contaminated with C. africana spores were released for 12 or 48 h in cages containing healthy greenhouse- or field-grown male-sterile sorghum plants at anthesis, the levels of ergot severities on the panicles ranged from 0.5–90%, per panicle. The levels of ergot infection on greenhouse- and field-grown AT×623 exposed to ergot contaminated field-trapped males for 48 h ranged from 0–81.7%. Mean external contamination of laboratory-reared and field-trapped moths placed in a soapy wash was 1.4 × 105 and 4.7 ×104 conidia/ml, respectively. This study demonstrated that contaminated adult corn earworm could transmit the sorghum ergot from diseased to healthy panicles when environmental conditions are favorable for infection. Thus, migrating moths and other highly mobile pest species have the potential to transport C. africana over relatively large distances.