Efficacy of Exserohilum monoceras, a potential fungi for biocontrol of Echinochloa spesies

Indigenous Exserohilum monoceras isolate 1125 was evaluated for its efficacy on different Echinochloa species. Exserohilum monoceras spores, prepared at 103, 104, 105, 106 and 107 spores/ml concentrations and sprayed onto E. crus-galli, showed increased infectivity with increasing spore concentration. Disease progress of E. crus-galli at various leaf development stages revealed the highest area under the disease progress curve (AUDPC) was at the 4-leaf stage (535.69 unit2), followed by the 3-leaf (446.75 unit2), 2-leaf (377.22 unit2) and 6-leaf stage (263.72 unit2). The fungus was also tested on 4 species of Echinochloa. The results showed that the AUDPC was highest for E. crus- galli var formosensis (693.33 unit2), followed by E. crus-galli var crus-galli (638.33 unit2), E. oryzicola (470 unit2) and E. colona (447 unit2). The study illustrated that E. monoceras is a potential fungus for biological control that can be further developed into bioherbicide

PHYTOTOXICITY AND FIELD EFFICACY OF EXSEROHILUM LONGIROSTRA JC/MIN THE CONTROL OF BARNYARDGRASS ECOTYPES (ECHINOCHLOA CRUS-GALLI VAR. CRUS-GALLI(L.) BEAUV)

Five selected ecotypes of bamyardgrass (Echinochloa crus-galli var. crus-gatti) from several rice growing areas in Malaysia and Indonesia were tested for their susceptibility  to the potential bioherbicide  (Exserohilum longirostratum). Bamyardgrass seedlings at the 2-3-lcaf stage were treated with 2.5xl07 conidia/ml from E. longirostratum  at different application frequencies (single, double and triple). In addition, aqueous extract assays were evaluated for the presence of a phytotoxic compound responsible for the virulence of the bioherbicide. Results of the study showed that disease severity significantly increased 20 days after treatment and resulted in mortality of the seedlings. Ecotypes from Perak and Lampung were most susceptible to the bioherbicide upon triple applications. Percentage dry weight reductions were 86.34 and 83.14%, respectively. Other ecotypes (Melaka, Banten and South Sulawesi) were observed to have a relatively similar response. Moreover, aqueous extracts of E. longirostratum  increased mortality up to 92.50% of bamyardgrass seedlings. These findings suggest that regular (double and triple) applications of E. longirostratum at a concentration of 2.5xl07 conidia/ml significantly increased mortality among bamyardgrass ecotypes. Mortality of the seedlings was attributed to the presence of a secondary phytotoxic metabolite. Key words :    Field efficacy / Phytotoxicity / Exserohilum longirostratum I Echinochloa crus-galli var. crusgalli I ecotypes

Host range of Exserohilum monoceras 1125, a potential biological control agent for Echinochloa spp.

A total of 54 plant species, including varieties and breeding lines from 14 families and 33 genera were screened against Exserohilum monoceras, a fungal pathogen with potential as biocontrol agent for barnyard grass, Echinochloa crus-galli. The selected plant species were treated with spore suspensions at about 2.5 x 107 spores/ml concentration in glasshouse conditions supplemented with 24 h dew. The ability of the fungus to infect the plants was evaluated by disease incidence and disease severity which translated into disease index (DI). The disease index of Echinochloa crus-galli var. crus-galli, E. crus-galli var. formosensis and E. stagnina were 4 (dead) while those for E. colona and E. oryzicola were 3 (severely damage). Among the economic plants tested, only Zea mays was infected with a disease index of 2 (tolerant). Young Imperata cylindrica was dead (DI = 4), however the older plant showed hypersensitive reaction (DI = 2). Other plants that were infected were Cymbopogon sp. (DI = 1), Paspalum sp. (DI = 3) and Rhynchelytrum repen (DI = 3). Exserohilum monoceras did not infect selected varieties of rice in Malaysia, such as MRQ 50, MRQ 74, MR 219, MR 220 and MR 84. Vegetables and medicinal plants used in the test were also not infected

Survey and evaluation of native fungal pathogens for biocontrol of barnyard grass (Echinochloa crus-galli complex)

Echinochloa crus-galli is reported to be among the three most serious weeds of rice in many countries in Asia. In Malaysia, yield loss by E. crus-galli was about 41%. Selective chemical herbicides are primary means to control the grass. However, the extended use of the herbicides may develop negative implication to the environment and public health. Several fungal pathogens have been reported to attack barnyard grass (E. crus-galli complex) in various parts of the world. This study was to isolate, identify and evaluate the native fungi from diseased barnyard grass in paddy field, for potential as bioherbicide. From surveys carried out in 2003 to 2004 throughout the Peninsular Malaysia, several fungi species were identified to be associated with the diseases. A total of 82 isolates from 12 fungus genera have been isolated. Among the fungi were E. monoceras, E. longirostratum and Curvularia lunata. The fungus, E. monoceras, was consistently found associated with the disease, virulent, stable and has the ability to produce spores profusely in culture. These characteristics suggest that it can be used as biological control agent for the grass

Effects of moisture duration and temperature on infection of Exserohilum monoceras on Echinochloa crus-galli at different growth stages

The effects of moisture duration and temperature on the infectivity of Exserohilum monoceras on Echinochloa crus-galli, an important weed in Malaysian granaries, were investigated. The results showed that E. monoceras infections were influenced by the availability of moisture and temperature. The fungus needed a minimum of 12 h of humidity to cause severe disease on the host. The apparent disease infection rate was also influenced by moisture duration exposed to the plants. The fastest apparent infection rate was observed at 24 h of moisture exposure for 2-leaf plants (rL = 0.74 logit/day) and 6-leaf plants (rL = 0.72 logit/day). The optimum temperature for infection was within the range of 25 – 35 °C. The study indicated that temperature also influenced the ability of the fungus to infect E. crus-galli. The apparent infection rate for 4-leaf plants at 25 °C was rL = 1.05 logit/day, 30 °C at rL = 1.0 logit/day and 35 °C at rL = 0.77 logit/day. It could be taken as an advantage particularly in Malaysia where the temperature in granary areas usually ranges from 27 – 37 °C. Based on the results of this study, E. monoceras can be exploited as a bioherbicide, if the constraints related to moisture dependency can be solved

Field efficacy of Exserohilum prolatum-a potential mycoherbicide for biological control of itchgrass (Rottboellia cochinchinensis)

The experiments were conducted to evaluate the potential of the Exserohilum prolatum as a mycoherbicide for the itchgrass (Rottboellia cochinchinensis) control under natural conditions in two field experiments in a non crop situation and in association with a maize crop. Three doses were (single, double and triple) applied to the main plots with 2 week intervals. The sub-plot treatments were distilled water solution (check), the Exserohilum prolatum conidial concentration of 2x107, 2x108 and 2x109 conidial mL-1 or glyphosate (N-(phosphonomethyl) glycine) herbicide as control check. Disease severity was rated at 5 day intervals after application and the area under disease progress curve (AUDPC) was calculated for each treatment. The above ground parts of the itchgrass and maize were recorded at the end of the experiment. The results showed that application frequency and inoculum concentration greatly influence the itchgrass control. Significantly higher percentage control of the itchgrass were recorded from triple application frequencies (90.4%) compared to single (62.4%) and double (70.4%) applications. Within the three frequencies of application, increasing inoculum concentration increased the itchgrass control from between 53 to 90.4% compared to untreated check. The results indicate that the E. prolatum has a good potential as a biocontrol agent for the itchgrass

Ecological and socioeconomic impacts of invasive alien species in island ecosystems

Minimizing the impact of invasive alien species (IAS) on islands and elsewhere requires researchers to provide cogent information on the environmental and socioeconomic consequences of IAS to the public and policy makers. Unfortunately, this information has not been readily available owing to a paucity of scientific research and the failure of the scientific community to make their findings readily available to decision makers. This review explores the vulnerability of islands to biological invasion, reports on environmental and socioeconomic impacts of IAS on islands and provides guidance and information on technical resources that can help minimize the effects of IAS in island ecosystems. This assessment is intended to provide a holistic perspective on island-IAS dynamics, enable biologists and social scientists to identify information gaps that warrant further research and serve as a primer for policy makers seeking to minimize the impact of IAS on island systems. Case studies have been selected to reflect the most scientifically-reliable information on the impacts of IAS on islands. Sufficient evidence has emerged to conclude that IAS are the most significant drivers of population declines and species extinctions in island ecosystems worldwide. Clearly, IAS can also have significant socioeconomic impacts directly (for example human health) and indirectly through their effects on ecosystem goods and services.These impacts are manifest at all ecological levels and affect the poorest, as well as richest, island nations. The measures needed to prevent and minimize the impacts of IAS on island ecosystems are generally known. However, many island nations and territories lack the scientific and technical information, infrastructure and human and financial resources necessary to adequately address the problems caused by IAS. Because every nation is an exporter and importer of goods and services, every nation is also a facilitator and victim of the invasion of alien species.Wealthy nations therefore need to help raise the capacity of island nations and territories to minimize the spread and impact of IAS