🪱 Aphelenchid Nematodes -- Foliar, Mushroom, and Red Ring

In the previous lesson, we covered the citrus nematode -- a semi-endoparasite of roots. Now we shift to nematodes that break the underground rule entirely: the aphelenchid nematodes parasitise leaves, buds, seeds, and even tree trunks.

While most plant parasitic nematodes attack roots hidden underground, the aphelenchid nematodes parasitise above-ground plant parts. A rice farmer noticing bleached white leaf tips, a chrysanthemum grower finding deformed flowers, or a mushroom producer watching his yield collapse -- all may be dealing with nematodes from this unique group. Their above-ground habits require completely different management approaches.

This lesson covers:

1. White tip disease of rice -- A. besseyi, seed-borne
2. Mushroom nematode -- A. composticola, mycophagous
3. Foliar nematodes -- chrysanthemum and strawberry parasites
4. Red ring nematode -- R. cocophilus, insect-vectored, under quarantine

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Overview

• Aphelenchoides = resembling Aphelenchus; from Greek apheles (smooth) + enchus (stylet).
• Commonly called Leaf and Bud Nematodes or Foliar Nematodes.
• Unlike most PPNs that attack roots, these parasitise aerial plant parts.
• Among the economically important aphelenchids, Aphelenchoides is the principal genus reported from India.

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White Tip Disease of Rice

Causal Organism: Aphelenchoides besseyi

Feature	Details
First report (India)	Dastur, 1934 (epidemic form in Central Provinces, MP)
Distribution in India	Predominantly eastern and southern states
Disease type	Seed-borne -- nematodes survive in quiescent stage between glumes and grain
Feeding type	Ectoparasite (feeds from outside plant surface)
Spread favoured by	High humidity (nematodes need moisture film to move on plant surfaces)

Diagnostic Symptom

The upper 3--5 cm of the leaf tip turns white or pale yellow at the tillering stage -- the hallmark symptom giving the disease its name.