Mode of Entry of Bacteria in Plants
Unlike fungal pathogens, bacteria are incapable of mechanically penetrating the cultinized plant tissues, culticle, periderm, etc. Since the ability to form appresoria is lacking in them. The ways of gaining entry into the plants are as follows.
1. Active invasion by bacteria through non-cultinized surface is sometimes feasible by means of a large mass of cells functioning together. Rhizobium spp. Which causes nodules in legume form a muciliagenous bacterial colony or zoogloea at the apex of the root hairs or root tips, the Zoogloea dissolves the cell wall and then, in the form of a curved and branched infection filament or infection thread advances into the interior of root hair and hence, into the root corner.
2. The cells of black rot of caggage, Xanthomonas campestris, enter through hydathodes, which are specialized gland cells at leaf edge.
3. The fire blight bacterium, Erwinia amylovora, enters the floral parts through the special nectar producing cells present system.
4. The potato scab organism, Streptomyces scabies, gains entry into the tubers through lenticels.
5. Entry through stomata: The mechanism of entry into the stomato is through water congestion which leads the cells into the open stomato assisted by wind blown rain or dew.
e.g 1. Pseudomonas tabaci causing wild fire of tobacco.
2. Xanthomonas. campestris pv. malvacearum causing angular leaf spot of cotton.
3. Xanthomonas. Phaseoli causing bean blight.
4. Xanthomonas. Campestris causing black rot of cabbage.
6. Entry through Wounds:
During various cultivation operations and while harvest, transport and storage, injuries to various plants parts are caused. Many bacteria present in vicinity enter the host tissue.
E .g Erwinia spp. causing soft rot of vegetables.
Agrobacterium tumefaciens causing crown gall of fruit trees.
7. Entry through Insect Wounds:
E. g Crown gall of fruit trees and wilt of cucumber.
8. Entry through wounds caused by plant parasitic nematodes and funi. Root disease complex in citrus.