Etiology and control of the following Potato diseases: Early blight, Late blight, PSTV (Potato Spindle Tuber Viroid)
Early Blight of Potato:-
Pathogen:- Alternaria solani
Symptoms:-
> It is present in both hills & plains.
> Brown-black necrotic spot-angular, oval shape characterized by concentric rings.
> Several spot coalesce & spread all over the leaf.
> Shot holes on fruits.
Management:-
> Disease free seed tubers should be used for planting.
> Removal and destruction of infected plant debris should be done because the spores lying in the soil are the primary source of infection.
> Very early spraying with Zineb or captan 0.2% and repeating it for every 15 – 20 days gives effective control.
> The variety Kufri Sindhuri possesses a fair degree of resistance.
Late Blight of Potato:-
Pathogen:- Phytopthora infestans
Symptoms:-
> It affects leaves, stems and tubers.
> Water soaked spots appear on leaves, increase in size, turn purple brown& finally black colour
> White growth develops on under surface of leaves.
> This spreads to petioles, rachis& stems.
> It frequently develops at nodes.
> Stem breaks at these points and the plant topples over. In tubers, purplish brown spots and spread to the entire surface on cutting, the affected tuber show rusty brown necrosis spreading from surface to the center.
Management:-
> Protective spraying with mancozeb or zineb 0.2 % should be done to prevent infection of tubers.
> Tuber contamination is minimized if injuries are avoided at harvest time and storing of visibly infected tubers before storage.
> The resistant varities recommended for cultivation are Kufri Naveen, Kufri Jeevan, Kufri Alenkar, Kufri Khasi Garo and Kufri Moti.
> Destruction of the foliage few days before harvest is beneficial and this is accomplished by spraying with suitable herbicide.
Potato Spindle Tuber Viroid (PSTV):-
Pathogen:-
> Potato Spindle Tuber Viroid (PSTV) is an EU listed quarantine pathogen of potatoes which causes stunting of the plant and malformation and cracking of tubers.
> The main host is potatoes but the disease also affects tomatoes and solanaceous ornamentals.
Symptoms:-
> Mild strains generally cause no obvious symptoms in potatoes.
> However severe strains in sensitive cultivars may cause foliage to be spindly, very upright, with overlapping leaflets and sometimes with upward rolling of terminal leaflets.
> Plants will be stunted.
> Tubers may show the following deformities; small, elongated, cylindrical, spindle or dumb-bell-shaped, with prominent eyes evenly distributed over the tuber, and cracking.
> Sprouting is slower than in healthy tubers.
Management:-
> There are no chemical or biological controls available to control PSTV within infected plants. Therefore control is essentially through the use of healthy virus-free seeds or planting material, and good crop sanitation practices.
> If infection does occur, destruction of infected plants and strict hygiene measures to prevent infection of subsequent crops are the only courses of action.