Ahmad S. Al-Hazmi

Damage potential and reproduction of Heterodera avenae on wheat and barley under Saudi field conditions

This study was conducted to determine the effect of H. avenae initial population densities ( Pi ) on the yield of wheat (two growing seasons) and barley (one season) and on nematode reproduction, under Saudi field conditions. At increasing Pi, H. avenae suppressed ( P lessequal 0.05) the number of spikes, weight of spikes, weight of 1000 kernels, grain yield and straw yield of wheat and barley. Grain yields were reduced by 40 to 92% for wheat (during the two seasons) and 17 to 77% for barley. Straw yields were also reduced, by 50 to 85 for wheat and 30 to 77% for barley. As Pi increased, final populations of H. avenae increased ( P lessequal 0.05) on both hosts, but the nematode reproduction factor ( Rf ) decreased. Significant negative linear regressions were obtained between H. avenae Pi and grain yield of wheat and barley. Final populations ( Pf ) were positively correlated with Pi on wheat and on barley. Rf was negatively correlated with Pi on wheat and barley. Schadigungspotential und Vermehrung von Heterodera avenae an Weizen und Gerste unter Freilandbedingungen in Saudiarabien - Die vorliegende Untersuchung wurde durchgefuhrt, um die Wirkung unterschiedlicher Ausgangspopulationen ( Pi ) von Heterodera avenae auf den Ertrag von Weizen (zwei Vegetationsperioden) und Gerste (eine Vegetationsperiode) sowie auf die Vermehrung der Nematoden unter saudiarabishen Freilandbedingungen zu ermitteln. Bei steigender Pi verminderte ( P lessequal 0.05) H. avenae die Anzahl der Ahren, das Ahrengewicht, das Tausendkorngewicht, den Korn- und den Strohertrag von Weizen und Gerste. Die Kornertrage wurden bei Weizen (zwei Vegetationsperioden) um 40-92% vermindert, bei Gerste um 17-77%. Auch die Strohertrage gingen zuruck, bei Weizen um 50-85% und bei Gerste um 30-77%. Mit zunehmender Pi stiegen die Endpopulationsdichten von H. avenae bei beiden Wirtspflanzen an ( P lessequal 0.05), doch nahm der Vermehrungsfaktor ( Rf ) der Nematoden ab. Zwischen Pi von H. avenae und dem Kornertrag von Weizen und Gerste wurden signifikante negative Regressionen erhalten. Die Endpopulationen ( Pf ) waren an Weizen und Gerste positiv korreliert mit Pi . Rf war an Weizen und Gerste negativ korreliert mit Pi .

Pathotype characterisation of the cereal cyst nematode, Heterodera avenae, in Saudi Arabia

Al-Hazmi, A. S., Cook, R., Ibrahim, A. A. M. (2001). Pathotype characterisation of the cereal cyst nematode, Heterodera avenae, in Saudi Arabia. Nematology, 3, (4), 379-382.

Effects of different inoculum densities of Trichoderma harzianum and Trichoderma viride against Meloidogyne javanica on tomato

A greenhouse experiment was conducted to evaluate the effects of different inoculum densities of two Saudi isolates of Trichoderma harzianum and Trichoderma viride against Meloidogyne javanica on tomato. Four densities (104, 106, 108 and 1010 spores/g of soil) of each fungus were used. The results indicate that all four inoculum densities of the two Trichoderma species suppressed the nematode reproduction and root galling; and increased the growth of tomato plants, compared to controls. Efficacy of both fungi increased as their inoculum densities increased. Generally, efficacy of T. harzianum was better than that of T. viride, especially at the highest used density (1010 spore/g soil) which resulted in the best control.

Interaction between Meloidogyne incognita and Rhizoctonia solani on green beans.

The interaction between Meloidogyne incognita (race 2) and Rhizoctonia solani (AG 4) in a root rot disease complex of green beans (Phaseolus vulgaris) was examined in a greenhouse pot experiment. Three week-old seedlings (cv. Contender) were inoculated with the nematode and/or the fungus in different combinations and sequences. Two months after last nematode inoculation, the test was terminated and data were recorded. The synchronized inoculation by both pathogens (N + F) increased the index of Rhizoctonia root rot and the number of root galls; and suppressed plant growth, compared to controls. However, the severity of root rot and suppression of plant growth were greater and more evident when inoculation by the nematode preceded the fungus (N → F) by two weeks. Nematode reproduction (eggs/g root) was adversely affected by the presence of the fungus except by the synchronized inoculation. When inoculation by nematode preceded the fungus, plant growth was severely suppressed and roots were highly damaged and rotted leading to a decrease of root galls and eggs.

Comparative efficacy of different approaches to managing Meloidogyne incognita on green bean

A greenhouse study was conducted to compare the relative efficacy of different approaches to managing Meloidogyne incognita on green bean. These approaches included chemical (fumigant, non-fumigant, seed dressing, and seed dip), biological (the egg-parasitic fungus, Paecilomyces lilacinus and the mycorrhizal fungus Glomus sp.), physical (soil solarization), and cultural (chicken litter and urea) methods. Accordingly, nine different control materials and application methods plus nematode-infected and non-infected controls were compared. Two important parameters were considered: plant response (plant growth and root galling) and nematode reproduction (production of eggs and the reproduction factor Rf). The results showed that the use of chicken litter as an organic fertilizer severely affected the growth and survival of the plants. Therefore, this treatment was removed from the evaluation test. All of the other eight treatments were found to be effective against nematode reproduction, but with different levels of efficacy. The eight treatments decreased (38.9–99.8%) root galling, increased plant growth and suppressed nematode reproduction. Based on three important criteria, namely, gall index (GI), egg mass index (EMI), and nematode reproduction factor (RF), the tested materials and methods were categorized into three groups according to their relative control efficacy under the applied test conditions. The three groups were as follows: (1) the relatively high effective group (GI = 1.0–1.4, Rf = 0.07–0.01), which included the fumigant dazomet, the non-fumigant fenamiphos, soil solarization, and seed dip with fenamiphos; (2) the relatively moderate effective group (GI = 3.4–4.0, Rf = 0.24–0.60), which included seed dressing with fenamiphos and urea; and (3) the relatively less effective group (GI = 5.0, Rf = 32.2–37.2), which included P. lilacinus and Glomus sp.

Influence of soil texture and moisture on the interaction of Meloidogynejavanica and Macrophominaphaseolina on green beans

Root-knot/charcoal root rot disease complex caused by the interaction of Meloidogyne javanica and Macrophomina phaseolina is a serious disease complex attacking bean crop either in the field or greenhouses. In two different greenhouse tests, the influence of soil texture and moisture on the severity of the root-knot/charcoal root rot disease complex on green beans, Phaseolus vulgaris were examined. Results of the soil texture test indicated that the disease severity (suppression of plant growth and rootknot/charcoal root rot disease index), the nematode reproduction and the fungus growth in soil increased with the increase of sand content in the soil. Results of the soil moisture test showed that the greatest plant damage occurred at the soil of moisture level of 30% of field capacity, and disease severity decreased gradually as the moisture level was increased. KEYWORDS