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Three isolates of Colletotrichum sublineolum P. Henn were inoculated on leaf blades and midribs of twenty-six johnsongrass cultivars with two sorghum cultivars, BTx 623 and SC 748-5 by using an excised leaf method. Phenotypic host responses from no response to severe infection, were observed. Some johnsongrass cultivars and BTx 623 showed different responses between the two tissues. Expression of six defense response related genes were measured using Real-time qRT-PCR. Leaf blade and midrib showed different patterns in BTx 623 inoculated with C. sublineolum; high expression of CHS8 and TLP were measured in midrib at 24 and 48 hpi respectively.

Sorghum accessions from Uganda were evaluated for grain mold and anthracnose resistance during the 2005 and 2006 growing seasons at the Texas A&M University Research Farm, near College Station, TX. Accession PI534117 and SC719-11E exhibited the lowest grain mold severities of 2.4, whereas, accessions PI534117, PI534144, PI576337, PI297199, PI533833, and PI297210, with SC748-5 were highly resistant to anthracnose in both years. Accessions PI534117, PI297134, PI297156 exhibited low grain mold severities in 2006. Significant negative correlation was recorded between grain mold and percent germination and high temperature in both years. In 2006, daily precipitation recorded significant positive correlation with grain mold. The seed mycoflora was analyzed across sorghum lines and treatments. In 2005, Curvularia lunata and Fusarium thapsinum were the most frequently recovered fungal species with 31 and 21% incidence, respectively, followed by Alternaria spp. (19%) and F. semitectum (13%). In 2006, predominant colonizers were F. thapsinum (58%), followed by Alternaria and F. semitectum with 15 and 10, percent respectively, while C. lunata had a 6% incidence. In this study, PI534117 holds promise for multiple disease resistance, as it had the lowest disease severity of grain mold and was highly resistant to anthracnose in both years. It also has a high germination rate, a high seed weight, and its short stature is more advantageous for the new A-line conversion program.

Cotton quality and yield are affected by several factors during the growing season. A soil inhabiting fungus, Verticillium dahliae Kleb., can cause substantial yield loss in cotton. A molecular mapping F2 population derived from the interspecific cross of the highly tolerant Gossypium barbadense cv. Pima S-7 and the susceptible G. hirsutum cv. Acala 44 was phenotyped for disease incidence and severity. Phenotyping of individual plant reactions to the disease was quantified using a set of growth parameters measured 3 weeks after inoculation. The F2 phenotypic distribution of these parameters (number of healthy leaves, node number, leaf weight, stem weight, and total shoot weight) suggested that resistance is polygenic inherited. Microsatellites were used to reveal polymorphism between resistant and susceptible parents. A total of 255 simple sequence repeat (SSR) primer pairs were screened over bulks constituted by 10 resistant and 10 susceptible progeny. Sixty markers were used to analyze quantitative trait loci (QTLs). Eleven linkage groups were constructed consisting of 35 markers and spanning 531 cM with an average distance of 15.17 cM. QTL analysis was performed with MapQTL and QTL Cartographer. MapQTL indicated that 15 markers have significant linkage associations and 9 were distributed to chromosomes 10, 11, 12, and 25. Interval mapping also indicated the most likely position of markers that are significant and located on linkage groups. Three loci (CM12, STS1, 3147-2) had large effect on resistance to Verticillium wilt. Two loci were located on LG-1 and one on LG-2 and both linkage groups are located on chromosome 11. # 2005 Elsevier Ireland Ltd. All rights reserved.

A new cotton variant with reduced levels of terpenoid aldehydes (sesquiterpenoids and sesterterpenoids (heliocides)) was isolated from the progeny of hemizygous cotton ( Gossypium hirsutum cv. Coker 312) transformed with antisense (+)-δ-cadinene synthase cDNA. Southern analysis of leaf DNA digested with Hin dIII, Pst or Kpn I restriction endonucleases did not detect any antisense cdn1-C1 DNA in the genome of the variant. The gossypol content in the seed of the variant was markedly lower than in the seed of T1 antisense plants. Eighty-nine percent of the variant seed had a 71.1% reduction in gossypol and the foliage of the variant plants showed a 70% reduction in gossypol and a 31% reduction in heliocides. Compared to non-transformed plants there was no reduction in the number of lysigenous glands in the seed of the variant. The cotton variant shows uncoupling of terpenoid aldehyde synthesis and gland formation. The cotton variant may have resulted from somaclonal variation occurring in the callus tissue during the transformation–regeneration process.

Grain mold of Sorghum bicolor is one of the leading constraints for the production of optimum quality sorghum grain worldwide. Differences in mold levels among different varieties grown in the same environment imply that genes play a role in controlling mold severity. In order to determine if genes that function in active defense responses also affect molding, panicles of resistant and susceptible cultivars were inoculated at anthesis with conidial suspensions of Fusarium thapsinum and Curvularia lunata, the fungi most often found in naturally infected grain. RNA was extracted from the immature floral tissues at various times following inoculation. Levels of mRNA for four known defense-response genes, phenylalanine ammonia lyase (PAL1-1), chalcone synthase (CHS2G), β-1,3-glucanase (GLUC2-1) and chitinase (CHIT25-1) were examined by hybridization to PCR generated clones of the respective genes. Expression of each gene increased rapidly following inoculation with either fungus. Although differences were seen in response to the two pathogens, the general pattern was similar in resistant and susceptible cultivars. The results imply that factors other than the level or timing of active defense responses account for the cultivar differences seen when the plants are challenged at the time of flowering.

Induction of genes needed to synthesize terpenoid compounds that have antifungal activity has previously been demonstrated to occur earlier in SBSI, a wilt resistant cotton cultivar, than in the susceptible cultivar, Rowden. In this study we have used cloned probes to test the same cultivars for induced expression of genes from other known defense response pathways. The time course of mRNA appearance was followed for up to 4 days in stele tissues of control plants and in plants inoculated with conidia of the wilt pathogen, Verticillium dahliae . Among genes that code for enzymes in the phenylpropanoid defense pathway, phenylalanine ammonia-lyase mRNA was constitutively expressed. Levels of mRNA transcripts coding for chalcone synthase, an enzyme required for flavonoid biosynthesis, and for caffeic-O-methyltransferase, an enzyme used in synthesis of lignin, were greatly elevated in inoculated plants as compared to water treated controls. Greater and/or earlier initial response was detected in the wilt resistant cultivar than in the susceptible cultivar. Among genes coding for enzymes that can degrade fungal cell walls, equivalent levels of β-1,3 glucanase mRNA were present in both fungal and water-treated plants. Chitinase mRNA synthesis was strongly induced in inoculated plants. Levels of message continued to increase in Rowden, but diminished rapidly after 48–60 h in SBSI.

Oligonucleotide primers made complementary to conserved sequences in phenylalanine ammonia-lyase (PAL) and chalcone synthase (CHS) genes previously cloned from other species were used to amplify segments of the corresponding genes from sorghum. Greater than 70% base sequence identity with homologous genes confirmed that a 535 bp clone (PAL1-1) and a 620 bp clone (CHS2G) were derived from the coding regions of PAL and CHS respectively. When used to probe genomic digests, the two clones detected 3 and 5EcoRI fragments, respectively. One fragment for each probe was polymorphic in the parents of a mapping population, permitting a locus for each gene to be located on a sorghum RFLP linkage map. RNA gel blot analyses were performed on extracts from control seedlings and from seedlings challenged with either of two fungal sorghum pathogens or a pathogen of maize that elicits a hypersensitive response in sorghum. Although low levels of PAL and CHS mRNA transcripts were present constitutively in the controls, both rapidly accumulated to high levels following inoculation with the maize pathogen,Bipolaris maydis, and decreasing amounts of mRNA were apparent by 120 h post-inoculation. Since challenge withSporisorium reilianumwas by needle inoculation, an additional control of mock inoculations was included for this pathogen. However, no differences in the amount of mRNA for either gene were detected over the sampling period, whether samples from uninoculated, mock inoculated or spore-inoculated seedlings were tested. Differences in the timing and level of mRNA accumulation were detected in seedlings after inoculation withPeronosclerospora sorghi. While seedlings of both resistant and susceptible cultivars accumulated higher levels of PAL and CHS mRNA than uninoculated controls, the accumulation of mRNA in resistant cultivars was higher and longer lasting than that in susceptible cultivars.

Three active transport systems for amino acids and another for glucose in germinated conidia of Neurospora were all inactivated during incubation with the sulfhydryl reagents N-ethylmaleimide, p-chloromercuribenzoate, and iodoacetamide. Where tested, the inactivation by p-chloromercuribenzoate was reversed by the action of dithiothreitol. However, two other sulfhydryl reagents, the chloromethyl ketone derivatives of leucine and lysine, were found to have differential effects on the various transport systems. Inactivation by these two compounds did not occur at the active site of the permeases by affinity labeling, suggesting differential availability of sulfhydryl groups among the transport systems. Also, inactivation by these reagents was greatly enhanced in the presence of p-chloromercuribenzoate.