Pathogenicity of field and laboratorygrown inoculum of Neonectria galligena on potted apple trees

European canker caused by Neonectria galligena is an important disease of apple trees worldwide In this study methods were developed for conidium production in culture and for testing the pathogenicity of N galligena Conidia produced in culture were one or twocelled while conidia collected from cankers were multicelled Isolate ICMP9472 produced enough conidia in culture to produce inoculum (210 5 conidia/ml) to test the pathogenicity in comparison with that of conidia harvested from apple cankers from Motueka (field inoculum) and a twodayold suspension of conidia from Motueka apple cankers on potted Royal Gala trees in a glasshouse under continual misting The germination rates of the three inocula were similar (5079) Two months after inoculation all inoculated wounds were infected regardless of inoculum source However cankers caused by field inoculum (fresh and two dayold) were significantly larger (average 108 mm and 106 mm respectively) than those caused by isolate ICMP9472 (51 mm) Six months after inoculation cankers caused by fresh field inoculum were significantly larger than those caused by 2dayold inoculum which were significantly larger than those caused by isolate ICMP9472 In addition cankers caused by fresh field inoculum were significantly more active than those caused by older field inoculum or isolate ICMP9472

VIRULENSI JAMUR ENTOMOPATOGEN BEAUVERIA BASSIANA (BALSAMO) VUILLEMIN (DEUTEROMYCOTINA: HYPHOMYCETES) TERHADAP KUTUDAUN (APHIS SPP.) DAN KEPIK HIJAU (NEZARA VIRIDULA)

Virulence of entomopathogenic fungi Beauveria bassiana (Balsamo) Vuillemin (Deuteromycotina: Hyphomycetes) on aphid (Aphis spp.) and green stink bug (Nezara viridula). This study was conducted at the Laboratory of Plant Pests and Diseases Department of Plant Protection Faculty of Agriculture, University of Lampung. It was aimed to test the virulence of field and commercial inoculum of B. bassiana on aphid and green stink bug. The field inoculum of B. bassiana was originated from infected grasshoppers and isolated in Biocontrol Laboratory of PT Gunung Madu Plantations, Central Lampung, while the commercial inoculum (Natural BVR) was formulated by PT Natural Nusantara. A single exposure concentration assay (1 x 107 conidia/ml) for each inoculum was conducted by immersing the insects in fungal suspension for 10 second. The results indicated that the virulence of field and commercial inoculum of B. bassiana was significantly different on aphid . The field inoculum B. bassiana was highly virulent and caused 78.8% mortality, on the contrary the commercial B. bassiana showed low virulence and caused only 27.42% mortality of aphid. However, both inocula caused 76% and 70% mortality on green stink bug respectively. The lethal period of the field and commercial B. bassiana are 3.70 days and 3.72 days respectively on aphid, and 5.44 days and 4.58 days on green stink bug. The virulence value of both inocula are 0.271 and 0.268 on aphids, and 0.195 and 0.245 on green stink bug. The virulence of both inocula is not significantly different. This results suggests that the commercial inoculum B. bassiana at 1 x 107 conidia/ml of concentration is less effective than the field inoculum B. bassiana as control agent on aphid.

Modeling Leaf Age-Related Susceptibility and Rust Eruption Dynamics in Peanut

To improve simulation of epidemics of peanut rust, information on the effects of leaf age and pustule eruption dynamics is needed. An analysis was made of the change of leaf susceptibility of rust with leaf aging using plants exposed to field inoculum. The youngest leaf was most susceptible to rust infection. As leaves aged, susceptibility decreased quickly. The relationship of infection frequency (Y, relative number of pustules) to leaf age (X, leaf position downward on the main stem) was described by a mathematical model Y = 2.17X(-0.83). The dynamics of pustule eruption also was studied using artificial inoculation. Analysis showed that after inoculation, pustule eruption over time was distributed in a logistic pattern. Rust eruption began at 130 and reach a peek at 250 rust degree days—that is, between 7 and 15 d after inoculation. Mathematical models of leaf age-related susceptibility and rust eruption dynamics will be incorporated into simulation model of rust epidemics.

The developing relationship between Stylosanthes and anthracnose after 14 years in a North Queensland pasture. 2. Diversity in the pathogen population

Broad diversity was indicated in fungal isolates of Colletotrichum gloeosporioides collected from a mixed accession Stylosanthes pasture during 1987-89. Isolate pathogenicity studies revealed 7 different pathogenic groups in 1987, while 16 different groups were separated in the 1989 collection. About 40% of isolates from both years were capable of producing symptoms on only 2 differential host lines while the more complex groups (pathogenic on 3-6 differentials) were proportionately less common. Fungal growth at 4 temperatures revealed significant variation in growth rates although most isolates grew optimally at 28�C. When 3 isolates representing different pathogenic groups were examined in a series of glasshouse inoculum composition studies, all contributed evenly to the number of lesions produced when inoculated together in equal proportions. There was no evidence of domination by the most virulent isolate used in these glasshouse studies and similarly there was no evidence of particular strain dominance in the field. Continual natural diluting of virulent field inoculum by the large diversity of other strains would probably prevent rapid severe epidemics developing in this pasture.

Survival of the take-all fungus in the presence and absence of susceptible grasses

A field trial was conducted to compare the effect of depth on inoculum of Gaeumannomyces graminis var. tritici under grasses and bare-fallow. Soil was sampled from 0-5, 5-10 and 10-15 cm depths in March, October and December 1986. Sample bioassays were carried out to determine infectivity, propagule number and to evaluate the contribution of different sized particles to the total soil-borne inoculum. A pot experiment examined the conduciveness of the respective soil samples to take-all. Grasses were effective in the carry-over of the field inoculum of the take-all fungus. In grass plots, infectivity was similar at the three sampling dates, although propagule number increased with time. In fallow plots, infectivity and propagule number declined progressively. Inoculum level fluctuated with time in both treatments, mainly in the 10-15 cm layer, and was most stable in fallow plots at 5-10 cm. Infectivity increased with increase in propagule size and the larger propagules were more infective at l2�C rather than 20�C. There was no difference between the conduciveness of soils from each layer in fallow plots, but in grass plots conduciveness increased with depth. Infectivity and propagule number of the fungus at respective depths appeared to be related to organic matter, conduciveness and fertility of the soil.

Corrigendum - Inoculation methods for assessing resistance in wheat to crown rot caused by Fusarium graminearum group 1

A range of inocululatron methods for assessing resistance in wheat to crown rot caused by Fusarium graminearum Group 1 was evaluated in the glasshouse and in the field. When grain was colonized with the pathogen, ground and applied with the seed at planting or spread around young plants as an aqueous suspension, high levels of crown rot were produced, but resistance (usually measured as per cent diseased plants or tillers) was still expressed. Similar results were achieved with induced field inoculum obtained by inoculating an area of wheat to obtain a high incidence of disease and incorporating the stubble into the soil. Natural field inoculum and inoculation of seed with spores produced lower levels of disease, although differentiation of resistant and susceptible cultivars was still possible. Other methods, suitable only for plants in pots and often for more specific purposes (for example, for inoculation at different stages of plant growth) were also studied. Resistance was best expressed where inoculum was applied onto or into soil, rather than directly onto or into plants. Currently, the resistance of all potential cultivars for release in Queensland is assessed in the field by sowing seed dusted with benomyl into furrows along which ground, colonized grain is distributed. Crown rot severity is then determined at maturity.

Inoculation methods for assessing resistance in wheat to crown rot caused by Fusarium graminearum group 1

A range of inocululatron methods for assessing resistance in wheat to crown rot caused by Fusarium graminearum Group 1 was evaluated in the glasshouse and in the field. When grain was colonized with the pathogen, ground and applied with the seed at planting or spread around young plants as an aqueous suspension, high levels of crown rot were produced, but resistance (usually measured as per cent diseased plants or tillers) was still expressed. Similar results were achieved with induced field inoculum obtained by inoculating an area of wheat to obtain a high incidence of disease and incorporating the stubble into the soil. Natural field inoculum and inoculation of seed with spores produced lower levels of disease, although differentiation of resistant and susceptible cultivars was still possible. Other methods, suitable only for plants in pots and often for more specific purposes (for example, for inoculation at different stages of plant growth) were also studied. Resistance was best expressed where inoculum was applied onto or into soil, rather than directly onto or into plants. Currently, the resistance of all potential cultivars for release in Queensland is assessed in the field by sowing seed dusted with benomyl into furrows along which ground, colonized grain is distributed. Crown rot severity is then determined at maturity.