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Galling Index | Purpose and Introduction


​​​This lab has two objectives. First, students will learn to identify the symptoms and signs caused by root-knot nematodes. Second, students will be able to evaluate disease severity using a rating scale system and critically evaluate the advantages​ and disadvantages of using such a system. 

​See instructors note #1 ​— Discussion of learning objectives


Root-knot nematodes (Meloidogyne spp.) have a wide host range and are major contributors to crop loss (Mitkowski and Abawi 2003). Following infection of host roots by second-stage juveniles (J2), Meloidogyne spp. establish a multinucleated feeding site called a giant cell where the nematode will molt three times before entering the adult reproductive stage. During post-infection development, Meloidogyne spp. females increase in width, eventually establishing a globose morphology. Feeding by the nematode induces plant cell hypertrophy leading to gall formation and reduced plant vigor.

Root-knot nematode infection is diagnosed through visual inspection of galls and microscopic examination for nematodes. A root-knot galling index is a scale-based evaluation of the severity of galling. Galling indices are used in both field and laboratory settings to quickly determine the presence and relative severity of root-knot nematode infection. Several different galling indices are available (Bridge and Page 1980; Zeck 1971; Barker et al. 1981). In this class, you will use a rating system based on a 0-10 scale.

or this laboratory, you will examine several plants previously infested with root-knot nematode. You will observe the symptoms and assign a rating to each plant based on the galling index. You will compare your galling index data with others in your class and propose methods to analyze the data. You will then remove and dissect a gall from one of the plants to look for the nematodes causing the disease.

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