Plant Pathology Science

 During recent years, citrus trees decline has becoming one of the most important factors of limiting the area of citrus orchards in the south of Iran including Fars province. Different biotic and abiotic agents were attributed to citrus decline worldwide, but it appears that some abiotic stresses including soil drought, and soil or water salinity, as well as some infectious diseases including gummosis, dieback, citrus nematode and witch’s broom are more important in Fars province. This is an attempt to gather information of the potential agents of complex diseases known as “citrus trees decline”, as well as, discussion on management strategies of citrus decline in Fars province.

 Introduction: Black cumin, an annual flowering plant in the family Ranunculaceae, is a medicinal herb with many pharmacological properties. Crown and root rot disease of this plant has been reported in most countries worldwide. This study was conducted to investigate the occurrence of this disease and identifying the causal agent in southwest of Iran. Materials and Methods: Black cumin farms were visited in Kohgiluyeh and Boyer-Ahmad province and southwest of Iran. Plants with crown and root rot were sampled. Pieces of infected root and crown were washed with tap water, dry blotted and plated on CMA-PARP. In total, 17 isolates of two different fungus-like species were isolated from rotted root and crown. Species identification was done based on morphological characteristics and temperature requirement. Pathogenicity test of the isolates were done on 3-week-old seedlings of Baft cultivar under greenhouse condition. Results: Eleven isolates were identified as Pythium aphanidermatum and six isolates as Phytophthora drechsleri. Both of these fungus-like species were pathogenic on the tested black cumin variety. Conclusion: Crown and root rot disease is present in the farms of black cumin in the southwest of Iran. The causal agents of this disease were identified as Pythium aphanidermatum and Phytophthora drechsleri. The black cumin cultivar Baft is susceptible to these pathogens.

Oak charcoal rot is caused by two fungi, Biscogniauxia mediterranea and Obolarina persica. These fungi, which are opportunistic or secondary invaders and attack stressful trees, are one of the main problems of oak forests in Iran. The disease was first reported in 2011 in the northern forests on Quercus castaneifolia and Zelkova carpinifolia trees and then in the Zagros forests on Q. brantii tree. The disease has spread rapidly in the forests of the Zagros over the years. Symptoms of the disease include decay and death of trees, browning of leaves and early fall. Gum secretion on the branches and trunks of old trees and browning of wood texture and woody vessels can be seen up and down the height of the trunk. The morphological characteristics of pathogens, the spread and survival of pathogens, and disease management methods are described in this article.

Algae are the most important plant growth stimulants due to their high content of minerals, amino acids, vitamins and growth regulators such as auxin, cytokinin and gibberellin. Use of these stimuli in crops can improve rooting, yield, photosynthetic capacity and their resistance to pathogens. Application of algae (mainly seaweeds) against various plant diseases including bacterial, fungal, viral and nematode diseases as well as pests has been proven. Seaweeds are used as a powder or extract mixed with soil, or foliar spray to control of plant diseases. They are usually involved in controlling plant pathogens by inducing plant resistance, antagonistic activity by induced activity of other microorganisms, and enhancing plant growth. In general, seaweeds can be applied as biofertilizers, biostimulators and soil amendments in integrated plant diseases management programs.

By studying the structure of the nematode community, healthy and unhealthy soils can be identified in terms of biodiversity and nutrient network. This information is useful for managing soil nutrient networks. The study of the nematode population structure as a biological indicator of soil health is based on the assessment of biodiversity indices, nutrition groups, population dynamics, soil nutrient network profile, biomass and metabolic profile. Practical applications for studying the structure of nematode populations in agricultural and natural ecosystems are described.

Glume blotch caused by the fungus Parastagonospora nodorum is an important disease of bread and durum wheat. The disease reduces the quantity and quality of wheat product. Disease history, pathogen morphology, and disease management methods, including crop rotation, plowing, post-harvest collection of plant debris , weed control, healthy seed culture or seed disinfection with a systemic fungicide, and cultivation of resistant cultivars are described.

Introduction: Poaceous plants such as corn, wheat, barley, sorghum, oats and millet are an important part of agricultural ecosystems. Smuts are one of the most important fungal diseases of these plants, which often cause economic damage and the destruction of part or all of their yields. Materials and Methods: Poaceous smut infected plants in farms and pastures of Markazi and Lorestan provinces were sampled. Morphological characteristics of these fungi and their germination type of teliospores were studied with bright field and fluorescent microscopes and identified using valid keys. The phylogenetic relationship of these fungi with other smuts was also investigated based on ITS-rDNA region sequencing. Results: According to the type of host, morphological characteristics and mode of teliospores germination 12 species vs. U. maydis, U. hordei, U. turcomanica, U. avenae, U.nuda, U. bromivora, U. cynodontis, U. tritici, Tilletia laevis, Tilletia controversa Sporisorium reilianum and S. cruentum were diagnosed. The morphological characteristics and phylogenetic relationship of these fungi with other smuts are described. Conclusion: The smuts of poaceous plants in Markazi and Lorestan provinces include eight species of the genus Ustilago, two species of the genus Sporisorium and two species of the genus Tilletia.