Kithsiri Jayasena - Academia.edu (original) (raw)

Papers by Kithsiri Jayasena

Canadian journal of plant pathology, Oct 12, 2022

Plant Disease, 2000

During the 2000 spring season, tomatillo (Physalis ixocarpa) plants showing chlorotic streaks on ... more During the 2000 spring season, tomatillo (Physalis ixocarpa) plants showing chlorotic streaks on leaves were observed in an experimental plot of the University of Georgia's Coastal Plain Experiment Station in Tift County, GA. Leaf samples from 192 plants were collected. These included plants that had chlorotic streaks and those without obvious symptoms. Samples were tested by ELISA using a commercially available Tomato spotted wilt virus (TSWV) detection kit (Agdia Inc., Elkhart, IN). TSWV was found in 10 samples that had chlorotic streaks on leaves, and the remaining plants with no obvious symptoms were negative for TSWV. Infected plants were found in both cultivars, Verde Puebla and Toma Verde. The presence of the virus had no apparent effect on plant size or fruit appearance. TSWV infection of the ELISA-positive samples was further verified by immunocapture reverse transcription-polymerase chain reaction (IC-RT-PCR) (1). The primer pair (5′-ATGTCTAAGGTTAAGCTC-3′ and 5′ TTAAGC...

Some mounted ill.Bibliography: leaves 156-186ix, 186, 43 leaves, 35 leaves of plates : ill. (some... more Some mounted ill.Bibliography: leaves 156-186ix, 186, 43 leaves, 35 leaves of plates : ill. (some col.) ; 30 cm.Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Pathology, Waite Agricultural Research Institute, 198

Canadian journal of plant pathology, Aug 31, 2022

ABSTRACT Key Messages • Scald – risk likely to increase if significant areas of Granger barley ar... more ABSTRACT Key Messages • Scald – risk likely to increase if significant areas of Granger barley are sown. • Net type net blotch – risk not expected to change with the adoption of newer varieties. • Spot type net blotch – risk expected to continue to increase with greater plantings of Hindmarsh and La Trobe. • Powdery mildew – overall risk is expected to decline until new pathotypes become dominant. • Barley leaf rust – growing varieties with APR can reduce the risk, but fungicide spraying may still be required. • Barley and cereal yellow dwarf– risk expected to increase with increased plantings of Hindmarsh and La Trobe.

SummaryPowdery mildew caused byBlumeria graminisf. sp.hordei(Bgh) is a constant threat to barley ... more SummaryPowdery mildew caused byBlumeria graminisf. sp.hordei(Bgh) is a constant threat to barley production but is generally well controlled through combinations of host genetics and fungicides. An epidemic of barley powdery mildew was observed from 2007 to 2013 in the West Australian wheatbelt (WA). We collected isolates, examined their sensitivity to demethylation inhibitor (DMI) fungicides and sequenced the Cyp51B target gene. Five amino acid substitutions were found of which four were novel. A clear association was established between combinations of mutations and altered levels of resistance to DMIs. The most resistant genotypes increased in prevalence from 0 in 2009 to 16% in 2010 and 90% in 2011. Yeast strains expressing theBghCyp51 genotypes replicated the altered sensitivity to various DMIs and these results were confirmed byin silicoprotein docking studies.

Fungicide Resistance in Plant Pathogens, 2015

The risk of fungicide resistance is greatest with pathogens with short dormant periods, with both... more The risk of fungicide resistance is greatest with pathogens with short dormant periods, with both sexual and asexual reproduction cycles, with large population sizes and when fungicides of a single mode of action (MOA) are repeatedly used. Most of the barley growing area in Western Australia (WA) has been seeded with powdery mildew (Blumeria graminis f. sp. hordei (Bgh)) susceptible cultivars for the last 10–15 years. Fungicides from the triazole group dominate the market and are used repeatedly as both seed and foliar treatments. Field failures have been observed leading to losses estimated at AU$100 m annually since 2007. Reduced efficacy has often been found to result from alterations in the gene encoding triazole target 14α-sterol demethylase (CYP51 syn. ERG11). Clear associations were found between accumulations of CYP51 mutations and reductions in triazole sensitivity. The combination of susceptible cultivars, conducive environmental conditions and repeated use of a single MOA has led with disappointing predictability to perhaps the most costly fungicide resistance epidemic in history.

ABSTRACT The barley powdery mildew pathogen, Blumeria graminis f. sp. hordei (Bgh), exists in num... more ABSTRACT The barley powdery mildew pathogen, Blumeria graminis f. sp. hordei (Bgh), exists in numerous haplotypes and displays significant differences in fungicide sensitivity. It causes considerable yield losses throughout the world. Microsatellite SSRs are useful tools to study the population level and biogeographic aspects of intraspecific diversity, but so far none have been defined for Bgh. Here, eight polymorphic microsatellite loci were identified and characterised. Primer pairs amplifying the loci were then applied to 111 isolates of Bgh from Australia. The number of alleles per locus ranged from 4 to 13, and Nei&#39;s genetic diversity ranged from 0.25 to 0.76. The microsatellite primers detected several clones among the isolates and defined 97 unique haplotypes. There was little evidence for regional genotypic subdivision, suggesting that gene flow may not be restricted among geographic regions. All data was consistent with high levels of genetic diversity, potentially resulting from random mating and spread within each region.This article is protected by copyright. All rights reserved.

Crop Protection, 2002

Ten fungicides (pyraclostrobin, tebuconazole, flutriafol, epoxiconazole, propiconazole, triadimef... more Ten fungicides (pyraclostrobin, tebuconazole, flutriafol, epoxiconazole, propiconazole, triadimefon, azoxystrobin, trifloxystrobin, difenoconazole and a mixture of propiconazole with iprodione) were evaluated as single applications for control of spot-type net blotch of barley caused by Drechslera teres f. maculata at three locations during 1999 and 2000. Under moderate disease severity, yield losses ranged from 17-19 per cent depending on location and under high disease severity, yield losses reached 32 per cent. Pyraclostrobin, propiconazole and a mixture of propiconazole with iprodione were the most effective in controlling disease, improving yield and grain quality. These fungicides show most promise as commercial treatments when yield and quality are taken into account. Azoxystrobin, trifloxystrobin, difenoconazole and epoxiconazole also provided disease control.

Australian Journal of Agricultural Research, 2005

Yield loss in wheat from natural infections with Puccinia graminis f.sp. tritici ranged from 10 t... more Yield loss in wheat from natural infections with Puccinia graminis f.sp. tritici ranged from 10 to 45% in 3 experiments over 2 years. Fungicide reduced subsequent stem rust severity on plant parts that were only slightly infected at the time of fungicide application, but was not effective on plant parts that were more heavily infected when treated. Fungicide control of stem rust was economic in a range of situations. Fungicide applied at head emergence with low disease incidence (5% of stems) increased yield by 0.3 t/ha. When applied prior to head emergence with high disease incidence at low disease severity, yield increased by 0.8–1.5 t/ha, depending on duration of control. At a high disease incidence and moderate disease severity, yield increases of 0.4–0.6 t/ha were observed. Grain quality was also significantly improved with fungicide. Fungicide was more effective when applied immediately following detection compared with a 3-week delay. Folicur was more effective at reducing di...

Australasian Plant Pathology, 2007

To study the loss of grain yield associated with specific levels of spot-type net blotch of barle... more To study the loss of grain yield associated with specific levels of spot-type net blotch of barley, experiments were conducted at three sites with between four and six different levels of application of the fungicide propiconazole or mixtures of propiconazole and iprodione applied to obtain a wide range of disease levels. Yield loss varied from 23 to 44%. There was

Australasian Plant Pathology, 2004

Pseudothecia carrying asci with mature ascospores of Drechslera teres f. maculata were isolated f... more Pseudothecia carrying asci with mature ascospores of Drechslera teres f. maculata were isolated from barley stubble from the southern part of Western Australia. Inoculation experiments were able to produce typical spot-type net blotch symptoms on the barley cultivar Gairdner. This is the first confirmed report of this teleomorph in Australia.

Powdery mildew (PM) is an issue for growing malting barley varieties in the high rainfall long se... more Powdery mildew (PM) is an issue for growing malting barley varieties in the high rainfall long season environment of southern Western Australia (WA). Most of the current popular varieties are susceptible to the disease. The disease is caused by fungus Blumeria graminis f. sp. hordei which survives in the previous seasons infected stubble and regrowth barley to infect unprotected susceptible barley crops.

Australasian Plant Pathology, 2006

Fungicidal control of Blumeria graminis f. sp. hordei occurring in barley late in the growing sea... more Fungicidal control of Blumeria graminis f. sp. hordei occurring in barley late in the growing season was examined in field experiments over 2 years. A single application of triazole fungicides at late booting (GS49) reduced powdery mildew severity and increased yield by 5-13%, depending on the season. Grain protein was slightly increased with fungicide treatment in one experiment whereas grain density and percentage screenings were not affected. Estimated profits from disease control with triazoles were 20−46/haformaltinggradebarleyinoneexperimentand20-46/ha for malting grade barley in one experiment and 20−46/haformaltinggradebarleyinoneexperimentand60-75/ha for feed grade barley in a second experiment. A strobilurin fungicide (azoxystrobin) had similar activity to that of triadimefon applied at the same rate. The results demonstrate economic control of powdery mildew in barley with the application of triazole fungicides when mildew is first detected around the booting stage of crop development in a disease prone environment.

Key Messages • Leaf rust pressure was moderate. • Varieties such as Bass which possess the Rph3 g... more Key Messages • Leaf rust pressure was moderate. • Varieties such as Bass which possess the Rph3 gene only, need to be managed with foliar fungicides to control leaf rust. • No fungicide responses were observed in varieties such as Flinders, Shepherd and Westminster, which possess the gene Rph20 in addition to other rust resistance genes. These varieties didn’t require foliar fungicides for leaf rust control in 2014. However in 2013, Flinders and Shepherd showed a marginal response to fungicides. No fungicide response in these two varieties in 2014 may be due to higher temperatures activating the genes. • Granger possesses an unidentified adult plant resistance gene in addition to two rust resistance genes and does not require fungicidal protection from leaf rust. • La Trobe showed a fungicide response even though the variety possesses gene suspected to be Rph20 in leaf rust control and increase in yield but the treatment differences between single and multiple foliar applications we...

Australian Journal of Agricultural Research, 2001

Medicago truncatula is used as a pasture legume and a source of nitrogen for grain crops in south... more Medicago truncatula is used as a pasture legume and a source of nitrogen for grain crops in southern Australia. Alfalfa mosaic virus (AMV) infection reduces herbage production and nodulation. The coat protein gene of a South Australian strain of AMV (AMV N20) has been transferred to Medicago truncatula cv. Jemalong 2HA using Agrobacterium-mediated transformation. The most detailed investigations were carried out with the coat protein gene in the sense orientation (CP+). Progeny (T1, T2, T3) raised from self-pollinated primary transformants (T0) containing the coat protein CP+ gene were resistant to AMV. Based on Southern analysis and segregation, the transformants contained a single gene copy. In the T3 generation, one line was immune and one line showed resistance to AMV N20. The immune line contained no detectable virus when plant sap from either inoculated or systemic leaves was bioassayed on Phaseolus vulgaris. This line was also immune to the heterologous AMV S40 isolate. A lin...