The book A Laboratory Guide for Identification of Plant Pathogenic Fungi is an indispensable resource for educators and students in the fields of botany, forestry, agriculture, vegetable sciences, silviculture, fodder, and pasture science, as well as those studying fungi that infect plants and crops for accurate identification. This comprehensive guide includes 14 chapters that cover fundamental fungal structures such as various types of mycelia, septa, sexual and asexual spores, sexual and asexual fruiting bodies, and specialized fungal structures for fungal genera and species. Additionally, it summarizes the different types of fungal disease symptoms on various plant parts, including the root, collar region, stem and twig, leaves, inflorescence, flower, and seed, along with the fungal genera and species responsible for causing them.
The book also provides information on the morphological characteristics used for fungal identification and the molecular techniques employed in such identification. As a result, this book is a crucial tool for identifying plant pathogenic fungi, and its absence previously hindered the practical training of students in many academic institutions. The availability of this resource will help to overcome this training deficit.
Humans encountered plant diseases during their nomadic lives and the early plant pathogens caused these diseases were fungal plant pathogens. These fungal pathogens attack almost all crops and plants by attacking different plant parts like root, trunk, stem, twigs, leaves, buds, inflorescence, flowers, fruits, and seed to cause different types of symptoms at the site of infection. The diseases are named on the basis of symptoms developed by fungal infection like damping off, seedling blight, wilt, root rot, collar rot, gummosis, twig blight, die-back, leaf spot, leaf blight, fire blight, rust, downy mildew, powdery mildew, smut, bunt, malformation, anthracnose, fruit rot, scab, pustules, seed rot, etc.
Fungi have been known to cause plant diseases in crops and plants of economic importance to humans since time immemorial. Ancient agriculture witnessed these plants’ sufferings but thought it was due to the curse of God on humans. The curiosity to know the causes of these crops and plant suffering developed the science of plant pathology and enlightened our understanding of the causes of these diseases. Among different plant pathogens, fungi occupy the prime position to cause plant diseases.
For visualization and identification of fungal specimens into their genus and species, the staining of the fungal specimens and their microscopy are necessary. The simple binocular microscope can be used for microscopy of the fungal specimens. 2.1. Stains to be Used in Microscopy 1. Methylene blue stain 2. Lacto phenol cotton blue stain 3. Crystal violet stain 4. Safranin
3.1. Terminology Used in the Description of the Fungal Pathogen 3.1.1. The Mycelium The hypha or mass of hyphae that make up the body of a fungus. 3.1.1.1. Coenocytic or aseptate mycelium
4.1. Damping Off 4.1.1. Pythium Pythium has filamentous (thread-like), hyaline, and coenocytic (non-septate) mycelial growth. The asexual or vegetative stage of Pythium produces sporangia (that germinate directly to produce a hypha or indirectly to give rise to a vesicle outside the sporangium, within which zoospores are formed) and sometimes hyphal swellings (spherical sporangia-like structures that do not give rise to zoospores).
5.1. Gummosis 5.1.1. Phytophthora\ Phytophtora citrophthora, Phytophtora nicotianae, Phytophtora syringae are the phytophthora species associated with citrus gummosis; while Phytophtora pistaciae sp. nov. and Phytophtora melonis are the principal causes of pistachio gummosis.
6.1. Leaf Spot, Blight, and Blast Leaf spots are irregular or round blemishes found on either side or both sides of the leaves. A typical spot is “zonal,” meaning it has a definite edge and a darker border. When lots of spots are present, they can grow together to cover the larger areas of the leaves. Different fungi are responsible for the leaf spots and sometimes a particular fungus causes a peculiar type of leaf spot and includes the fungi.
7.1. Die-Back 7.1.1. Colletotrichum The pathogen forms a large number of acervuli on the infected parts. The conidiophores are slightly curved, short, and club-shaped. The conidia are hyaline and falcate, borne singly on the conidiophores. Numerous black colored and thick-walled setae are also produced in acervulus. In culture, most isolates produce cottony, fluffy, or suppressed colonies (Fig. 7.1).
8.1. Malformation 8.1.1. Fusarium The classical example of Fusarium infection is Fusarium moniliforme which induces malformation in inflorescence, causing mango malformation disease. The fungal mycelial morphology may vary significantly on different media, and the descriptions here are based upon growth on potato flakes agar (PFA) at 25° C with on and off fluorescent light cycles of approximately 12 h each. The mycelial colony has rapid growth.
9.1. Fruit Spot and Blisters 9.1.1. Colletotrichum The pathogen forms papery or watery brownish areas at the site of infection, with a large number of acervuli on the infected parts. In the acervulus, the conidiophores are slightly curved, short, and club-shaped. The conidia are hyaline and falcate, borne singly on the conidiophores. Numerous black colored and thick-walled setae are also produced in the acervulus. In culture, most isolates produce cottony, fluffy, or suppressed colonies (Fig. 9.1).
10.1. Black Tip The black tip of grain infection is mostly observed on the wheat grains. The fungal pathogen involved in causing the black tip of grain includes the species of the fungal genus Alternaria and Helminthosporium. 10.1.1. Alternaria The genus stands distinct from other genera by its transversely and longitudinally septate (muriform) conidia. The conidia are usually formed in chains. These are dark brown, typically obclavate with a distinct oval body and beak.
11.1. Fruit Rots 11.1.1. Alternaria Please refer “Alternaria” section in Chapter 10. 11.1.2. Colletotrichum Please refer “Colletotrichum” section in Chapter 9. 11.1.3. Fusarium Please refer “Fusarium” section in Chapter 10.
12.1. Routine Media for Fungal Isolation In recent years commercially available readymade culture media have been used in research laboratories for the isolation of fungal plant pathogens. These culture media are standardized and they are in different types. Some media are used for general purposes while some others are used for the isolation and growth of specific pathogens e.g.
The pioneering German microbiologist, Robert Koch, identified a set of four conditions that need to be satisfied to establish that a particular organism is the causative agent of a particular disease. These conditions, known as Koch’s postulates, are: 1. The suspected pathogen must be found associated with the disease in all the diseased plants examined. 2. The organism must be isolated from the diseased tissue and grown in pure culture on nutrient media, with its characteristics described (non obligate parasites) or in a susceptible host plant (obligate parasites), and its appearance and effects recorded
In recent years several plant pathological laboratories have been using molecular techniques for identification of the fungal plant pathogens isolated from the diseased plants. These are specifically used for the confirmation of the pathogen identified based on their cultural and microscopic characteristics. With the help of fungal genomic studies, not only the genus but also the species of the pathogen is identified based on the genomic sequences available with NCBI, and provide the accurate identification of the fungal isolate. This identification method involves the following steps:a
1. Units of Measurements 1.1 Decimal fractions 1.2 Molar concentration 1.3 Weights 1.4 Volume
