Home › Growing Techniques › Article

Symptom Identification and Control Methods for Cotton Brown Spot Disease

Growing Techniques 0 views
Symptoms The disease mainly affects leaves. When cotyledons are infected, pinpoint-sized purplish-red spots first appear, then expand into brown, purplish-edged, slightly raised round to irregular lesions; multiple lesions merge together to form large patches, with small black dots scattered in the center, which are the pathogen's pycnidia. The center of the lesion easily breaks off and falls out, forming holes, and in severe cases the leaves drop off. On true leaves, the lesions are round, yellowish-brown, with purplish-red edges. Pathogen Phyllosticta gossypina Ell. et Mart., called cotton Phyllosticta leaf spot

Symptoms The disease mainly affects leaves. When cotyledons are infected, pinpoint-sized purplish-red spots first appear, then expand into brown, purplish-edged, slightly raised round to irregular lesions; multiple lesions merge together to form large patches, with small black dots scattered in the center, which are the pathogen's pycnidia. The center of the lesion easily breaks off and falls out, forming holes, and in severe cases the leaves drop off. On true leaves, the lesions are round, yellowish-brown, with purplish-red edges.

Pathogen Phyllosticta gossypina Ell. et Mart., called cotton Phyllosticta leaf spot fungus, and P. malkoffii Bubak., called Malkoff's Phyllosticta, both belong to the Fungi Imperfecti, subphylum Deuteromycotina. The pycnidia of both fungi are embedded in the leaf tissue. The former is spherical and yellowish-brown, 93.8 μm high, 85.7 μm in diameter, with an apical ostiole 18 μm in diameter, dark brown. The conidia are ovoid to elliptical, each with one oil droplet at each end, 4.8-7.9 μm long and 2.4-3.8 μm wide. The conidia of P. malkoffii are elliptical to short cylindrical, measuring 7.04-9.28 x 3.63-4.5 (μm), also with 2 oil droplets.

Transmission routes and disease conditions Both pathogens overwinter as mycelium and pycnidia on diseased plant debris. The following year, large numbers of conidia are released from the pycnidia and spread by wind and rain; the spores germinate under high humidity conditions. When the first true leaf of cotton has just emerged, if low temperatures and rain occur, the seedlings grow weakly and are prone to the disease.

For control methods, see cotton Alternaria leaf spot.

Related Articles