S. Bhuiyan

Efficacy, timing and method of application of fungicides for management of sorghum ergot caused by Claviceps africana

Trials conducted in Queensland, Australia between 1997 and 2002 demonstrated that fungicides belonging to the triazole group were the most effective in minimising the severity of infection of sorghum by Claviceps africana, the causal agent of sorghum ergot. Triadimenol (as Bayfidan 250EC) at 0.125 kg a.i./ha was the most effective fungicide. A combination of the systemic activated resistance compound acibenzolar-S-methyl (as Bion 50WG ) at 0.05 kg a. i./ha and mancozeb (as Penncozeb 750DF) at 1.5 kg a.i./ha has the potential to provide protection against the pathogen, should triazole-resistant isolates be detected. Timing and method of fungicide application are important. Our results suggest that the triazole fungicides have no systemic activity in sorghum panicles, necessitating the need for multiple applications from first anthesis to the end of flowering, whereas acibenzolar-S-methyl is most effective when applied 4 days before flowering. The flat fan nozzles tested in the trials provided higher levels of protection against C. africana and greater droplet deposition on panicles than the tested hollow cone nozzles. Application of triadimenol by a fixed wing aircraft was as efficacious as application through a tractor-mounted boom spray.

Factors influencing the germination of macroconidia and secondary conidia of Claviceps africana

The influences of temperature, time, and moisture on the germination of macroconidia and secondary conidia of Australian isolates of Claviceps africana were studied in vitro. The optimum temperature for germination of both macroconidia and secondary conidia of C. africana was 20degreesC. Although germination of macroconidia ceased near 31degreesC, approximately 30% of secondary conidia germinated at 37degreesC after 48 and 72 h of incubation. Sorghum flower extract agar stimulated macroconidium and secondary conidium germination, irrespective of temperature. Germination of macroconidia and secondary conidia on water agar started after 4 h of incubation at 20degreesC, reaching a maximum after 16-24 h and 14 h, respectively. Maximum germination of both macroconidia and secondary conidia was at greater than or equal to-5 bars at 20degreesC. Germination of secondary conidia ceased at -35 bars, whereas macroconidia germinated at water potentials as low as -55 bars at 20degreesC.

Mechanism of resistance in Australian sugarcane parent clones to smut and the effect of hot water treatment

Abstract. Resistance of sugarcane plants to smut is believed to be manifested by two mechanisms, (i) external resistance, governed by structural barrier of bud scale and/or chemical secretion from the bud, and (ii) internal resistance, regulated by interaction of plants and fungus within the plant tissue. Hot water treatments are routinely used to treat seed cane to eliminate a range of diseases including smut. It is believed that hot water treatment predisposes sugarcane plant to smut. This study was conducted to determine the resistance mechanisms of some important Australian parent clones, and their response to hot water treatment in relation to smut infection. Twenty-one clones, used regularly in the Australian sugarcane breeding program, were evaluated. Results showed that ∼47% of clones had external and 33% had internal resistance mechanisms, indicating that parent clones selected for this study possessed diverse mechanism of resistance. There is a possibility some or all clones with internal resistance mechanisms could also possess external resistance mechanism. Except one highly susceptible clone (Q205) in one trial, none of the clones subject to hot water treatment became more susceptible to smut. Although some clones showed increased resistance after hot water treatment. These findings will benefit breeders in selecting parent materials in their crossing programs to develop smut-resistant cultivars.

In vitro screening and evaluation of fungicides for the control of Claviceps africana on sorghum seed

Eleven fungicides, benomyl, bitertanol, captan, carbendazim, mancozeb, procymidone, propiconazole, tebuconazole, thiram, triadimenol and tridemorph, were tested in vitro at 50 and 10 mg a.i./L for their effects on the macroconidial germination of Claviceps africana, the sorghum ergot pathogen. Thiram and captan completely inhibited conidial germination of the two isolates (UQE1 and UQE2) tested. Nine of the best fungicides from this test were selected for assessment as seed treatments using sorghum seed which had been artificially coated with ergot honeydew containing macroconidia of the isolates UQEl or UQE9. Captan and thiram at 0.5, 1 and 2 g a.i./kg seed completely inhibited macroconidium germination of one isolate and reduced germination of the other to <0.2%. Thiram applied to honeydew-coated sorghum seed completely inhibited macroconidium germination at a rate lower than that currently registered (2.4 g a.i./kg) for use on sorghum seed in Australia. These results have important implications for the movement of sorghum seed from areas where C. africana is endemic to areas which are free from the pathogen.

Assessment of resistance to root-lesion and root-knot nematodes in Australian hybrid clones of sugarcane and its wild relatives

Root lesion nematode (Pratylenchus zeae) and root knot nematode (Meloidogyne javanica) are the two most important nematode pathogens of sugarcane in Australia. They cause significant yield loss but there are no known varieties with resistance. A research project commenced in 2011 to assess the level of nematode resistance in the progenies from clones derived from crosses between sugarcane (Saccharum spp.) and Erianthus spp. or Saccharum spontaneum Since standard methods of assessing nematode resistance in sugarcane clones were not available, the study aimed to develop rapid, effective and reliable methods for the screening of large numbers of clones for resistance to root lesion and root knot nematodes. A second objective was to determine the resistance of basic Saccharum spp., their wild relatives and some selected crosses to these two nematodes. Shoot and root biomass, reproduction factors (RF) and number of nematodes (or eggs) per g of roots were used to assess resistance levels. A visual rating of root galling was also used for root knot nematodes. The RF value, nematodes or eggs per g of roots, and visual rating (for root-knot nematode) were highly correlated. Resistant and susceptible clones were distinguished using any of these methods. It is concluded that the RF values can be used to detect nematode resistance in large numbers of clones. In the case of root-knot nematodes, visual gall ratings produced results that were similar to egg counts, and could be used as an alternative in future. For advanced clones, rating based on nematodes or eggs per g of root is likely to provide more accurate results. Basic S. spontaneum, E. arundinaceus clones and some progeny clones from crosses between these wild canes and commercial sugarcane clones, or from further backcrosses between these and sugarcane clones, were found to be resistant or moderately resistant to root-knot and root lesion-nematode. These clones are being further tested in the glasshouse and in the field, and should be useful sources of resistance for root-lesion and root-knot nematodes for sugarcane breeding programs.

New Method of Controlling Sugarcane Smut using Flutriafol Fungicide

Sugarcane smut, caused by Sporisorium scitamineum, is one of the most devastating diseases of sugarcane worldwide. Triazole fungicides such as propiconazole and triadimefon have been routinely used as dip treatments to protect seed-cane (stalk cuttings) from infection by sugarcane smut fungus. However, dip treatments can be applied only to mother stock (nursery) planting materials because of the logistics of dipping large quantities of seed-cane and it is difficult to dispose of the large volumes of waste fungicide solution in an environmentally safe manner. There was a need for a new fungicide that can be applied using more practical methods. The efficacy of flutriafol fungicide to control smut was evaluated in inoculated and infected stalks of a highly susceptible cultivar using various application methods. In a 2007 experiment, flutriafol fungicide was equally effective or better in controlling sugarcane smut as a dip than were two fungicides, propiconazole and triadimefon, registered in Australia. In 2009, two experiments determined the effectiveness of flutriafol when applied by mixing with fertilizer or spraying on the seed-cane at planting. All fungicide treatments significantly suppressed smut in one experiment but, in the second experiment, flutriafol-fertilizer mix treatments were ineffective. In 2010, two experiments verified the efficacy and effective rates of flutriafol against sugarcane smut when applied through existing spray equipment designed to spray fungicide on cuttings as they drop into the planting furrow on a commercial planter. Area under the disease progress curve values of smut incidence were reduced significantly to 47 and 56% with low (125 g a.i. ha-1) and high (375 g a.i. ha-1) application rates, respectively, in both experimental sites compared with the inoculated control plots. Sugar yield increased by 46 to 65% in one experiment and 157 to 203% in the second experiment compared with the inoculated control. This research formulated a more practical method of application of flutriafol and suggests greater applications of this fungicide for the management of sugarcane smut.

Effects of conidial concentration and stigma wetness period on infection by the sorghum ergot pathogen Claviceps africana

The effect of conidial concentration and length of stigma wetness period on infection of sorghum spikelets by Claviceps africana was studied in a controlled environment experiment. Aspore concentration of at least 106 conidia/mL was required for maximum infection on sorghum panicles. Maximum infection occurred during a stigma wetness period between 4.5 and 6 h. Approximately 11–15% infection occurred when stigmas had been dried immediately after inoculation. This study demonstrated that the stigma wetness is an important parameter in sorghum ergot epidemiology.

Iterative germination and innovative techniques for the production and inoculation of secondary conidia of sorghum ergot (Claviceps africana)

Abstract Five methods of harvesting pure secondary conidia were attempted, but only one was successful. The only successful method involved moving air across the surface of water agar plates or moist soil on which secondary sporulation was occurring at 0.2 – 3 m/s. Among the inoculation techniques, brushing the secondary conidia on to the wet stigma gave maximum ergot infection (80%) followed by brushing the secondary conidia on to the dry stigma (77%). Conidia of Claviceps africana produced up to seven generations of sibling conidia. The length and width of secondary conidia showed a reduction in size from 10.92 – 10.13 µm and 5.49 – 5.13 µm, respectively, across generations. However no definite trend in decline in size of secondary conidia was evident. The optimum temperature range for germination of secondary conidia of Australian isolates of C. africana is between 14.6 and 20°C.