Physiological Fitness Cost Associated with Glyphosate Resistance in Echinochloa colona: Seed Germination Ecology

The expression of fitness cost associated with herbicide resistance in weeds is not universal and may vary during different life stages. Hence, an analysis of the fitness cost of a glyphosate-resistant Echinochloa colona at the seed stage was conducted. Seed germination ecology of glyphosate-susceptible and - resistant E. colona was studied to examine the physiological fitness cost between the S (susceptible) and R (resistant) phenotypes. The plant material was selected from within one segregating glyphosateresistant E. colona population to minimise allelic interference from other fitness-related loci. Experiments were conducted in a growth incubator at alternating temperatures of 30/20C day/night with a 12-h photoperiod. Seed dormancy and germination were also tested under constant darkness at the same temperature regime. Seeds of both the S and R phenotypes kept at warmer temperatures (after-ripening dry storage at 15 to 35C) or on the ground surface outdoors for 14 days, germinated better (with more than 95% of seeds had germinated) than those seeds (about 20% germination) that were kept at lower temperature (8C) for the same period of storage. Light and longer dry after-ripening times increased the rate of seed dormancy release and germination (almost 100% seed germination) for both the S and R phenotypes. Equal decline in seedling emergence in both the S and R phenotypes was evident with increasing soil burial depth (P > 0.05). Thus, the S and R phenotypes exhibited similar characteristics of seed dormancy release, germination and seedling emergence. As there is lack of physiological fitness cost in the R phenotype of E. colona at the seed and early seedling stage, it remains a challenge to develop specific control measures for the R phenotype. An alternative herbicide with different mode of action should be integrated with other weed management approach such as cultural, mechanical and biological control to reduce sole reliance of glyphosate in controlling the R phenotype of this E. colona population.Fil: Sheng Goh, Sou. The Malaysian Rubber Board; MalasiaFil: Vila Aiub, Martin Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Busi, Roberto. University of Western Australia; AustraliaFil: Goggin, Danica. University of Western Australia; AustraliaFil: Powles, Stephen B.. University of Western Australia; Australi

Growth and yield performance of Hevea brasiliensis under various planting density

Rubber growing in Malaysia predominantly a smallholder’s industry with contributed about 93.1% (2013) of the total rubber production in Malaysia. Although there is an important contribution by the rubber smallholders sector, the majority of them to be plagued by persistent low productivity and income largely due to uneconomic size of holding, planting of non-recommended clones, low adoption of technology, capital deficiency and unstable of rubber price in the past. With the low yield of rubber (average 1400 kg per hectare, 2013) from the rubber smallholders, several approaches have been developed in Malaysia to increase land productivity and income. One of the approaches is through adopting high density planting. A study on the effect of high density planting on growth and yield of rubber was conducted in FELDA Jenderak Utara, Temerloh, Pahang, Malaysia, on Durian and Gajah Mati soil series, started in February 2000. The treatments study were (i) Planting densities, i.e. 500 trees/ha (4m x 5m), 700 trees/ha (4m x 3.6m), and 1000 trees/ha (4m x 2.5m) and (ii) rubber clones i.e. RRIM 2025, RRIM 2016 and RRIM 2001. The treatments were arranged according to the Split Randomized Complete Block Design (RCBD) with three replications. The results found there were significant effects of planting density and clone on growth (girth) of rubber, 63 months and 151 months after planting. For instance, the densities of 500 trees and 700 trees/ha had higher growth (girth) compared to density of 1000 trees/ha with mean of 47.4 cm = 47.2 cm > 44.1 cm, respectively, 63 months after planting. A similar result was found, 151 months after planting. Clone RRIM 2025 had higher growth (girth) compared to RRIM 2016 and RRIM 2001 with mean of 48.3 cm > 46 cm = 44.6 cm, respectively in the same period. The densities of 500 and 700 trees/ha produced higher tree productivity (g/t/t) at the second year of tapping compared to the density of 1000 trees/ha with means of 64.9 g/t/t = 64.2 g/t/t > 52.9 g/t/t, respectively with tapping system of 1/2S D3 SEN(8x/year). However, there was no significant effect of clone on tree productivity during the same period of tapping (RRIM 2025 = RRIM 2001 = RRIM 2016 with mean of 64.7 g/t/t = 60.3 g/t/t = 59.0 g/t/t, respectively). Survey on bark thickness was conducted, 151 months after planting. The result found, the density of 500 and 700 trees/ha had thicker bark thickness compared to the density of 1000 trees/ha with means of 10.9 mm =10.1 mm > 9.4mm, respectively. Density of 1000 trees/ha produced higher crotch height compared to the density of 700 trees/ha and 500 trees/ha with means 6.0 m > 4.4 m = 4.2m, 151 months after planting. However, no significant were found for the treatment clone and interaction of clone x density on crotch height. Clone RRIM 2025 produced higher clear bole volume compared to the clone RRIM 2016 and RRIM 2001 with means of 0.16 m3/tree > 0.13 m3/tree = 0.11 m3/tree, respectively

Glyphosate resistance in Echinochloa colona: phenotypic characterisation and quantification of selection intensity

BACKGROUND: A population of Echinochloa colona infesting agricultural fields in the northern region of Western Australia evolved glyphosate resistance after 10 years of glyphosate selection. This study identified two phenotypic (susceptible S versus resistant R) lines from within a segregating glyphosate-resistant population. Estimation of survival, growth and reproductive rates of the phenotypes in response to glyphosate selection helped to characterise the level of resistance, fitness and the selection intensity for glyphosate in this species. RESULTS: Estimations of LD50 (lethal dose) and GR50 (growth rate) showed an eightfold glyphosate resistance in this population. The resistant index based on the estimation of seed number (SYn50) showed a 13-fold resistance. As a result of linear combination of plant survival and fecundity rates, plant fitness values of 0.2 and 0.8 were estimated for the S and R phenotypes when exposed to the low dose of 270 g glyphosate ha−1. At the recommended dose of 540 g glyphosate ha−1, fitness significantly decreased (fivefold) in S plants but remained markedly similar (0.7) in plants of the R phenotype. Thus, the calculated selection intensity (SI) at 540 g glyphosate ha−1 was much greater (SI = 17) than at 270 g glyphosate ha−1 (SI = 4). CONCLUSIONS: The assessment of plant survival and fecundity in response to glyphosate selection in the S and R phenotypes allowed a greater accuracy in the estimation of population fitness of both phenotypes and thus of glyphosate selection intensity in E. colona. The estimation of seed number or mass of phenotypes under herbicide selection is a true ecological measure of resistance with implications for herbicide resistance evolution.Fil: Sheng Goh, Sou. University of Western Australia; AustraliaFil: Vila Aiub, Martin Miguel. University of Western Australia; Australia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Busi, Roberto. University of Western Australia; AustraliaFil: Powles, Stephen B.. University of Western Australia; Australi

Non-target-site glyphosate resistance in Echinochloa colona from Western Australia

An Echinochloa colona population from Western Australia has evolved resistance to glyphosate. This current study investigates the physiological, molecular and biochemical basis of glyphosate resistance in this population. To minimise genetic differences the susceptible (S) and resistance (R) phenotypes were isolated from within this resistant population. The S phenotype was found to accumulate significantly more shikimate in the leaf tissue than the R phenotype following glyphosate treatment. Target-site EPSPS gene sequencing revealed no resistance mutations and EPSPS gene expression was similar between the S and R phenotypes. Thus, glyphosate resistance in this population is unlikely target-site based. Similarly, there were no significant differences between the S and R phenotypes in glyphosate leaf uptake and translocation at the whole plant level. It is also unlikely that the resistance is associated with glyphosate metabolism as no major glyphosate metabolites were detected in leaf tissue of the S and R phenotypes. Despite much effort the exact glyphosate resistance mechanisms in this R population remain unclear, and novel resistance mechanisms are to be determined.Fil: Goh, Sou Sheng. Malaysian Rubber Board; Malasia. University of Western Australia; AustraliaFil: Yu, Qin. University of Western Australia; AustraliaFil: Han, Heping. University of Western Australia; AustraliaFil: Vila Aiub, Martin Miguel. University of Western Australia; Australia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Busi, Roberto. University of Western Australia; AustraliaFil: Powles, Stephen B.. University of Western Australia; Australi