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Undiagnosed root rot on onion in Tamil Nadu, India

A ProMED-mail post

<https://url.emailprotection.link/?bczGkw5NaxKViInVN3o8WI7SkfPjCplYcnrvkSnR7vDdzBseB4Z4JgOzMtf4NyhKwZ-87t_ekCqY4X1TR9IACFg~~>

ProMED-mail is a program of the International Society for Infectious Diseases <https://url.emailprotection.link/?bJcYJd1UM9bbZyueyHGqCfuWBsCz6JLr6QpMnBNG04Pz2V8akThtcwE1bjLVZbAR2-PZoubzhx-ALOhYt6Kir6w~~>

Date: Mon 1 Feb 2021 04:23 IST

Source: The Times of India, Times News Network (TNN) [edited] <https://url.emailprotection.link/?b68d-qHKQFwxzUgLb2tnRqOVT3gkKJgdXkhmripsHnNj7ZqzTP6kcEIjqawPjZyQvQHMz0mwvU-hXSUSqikue6QKxZDsfkkbb_O7o3Xnnl1sChavmZhuMmG2mHPB8hlKqHRkivzVCASkoytONqgdiC-hcUh28t_XEcjqgtwlxhT4~>

With onion crops on hundreds of acres damaged by rain and affected by root rotten disease in Perambalur district, farmers have started destroying the remaining standing crop. Those who took up cultivation during October-November [2020] suffered heavy loss due to incessant rain. "Most of the crops were affected by root rotten disease," said a farmer. Though they administered the prescribed pesticides and fertilizers, nothing could safeguard the crop, said another farmer.

Horticulture department officials have advocated taking up alternative cropping methods to avert diseases such as twister and root rot. Had the farmers done summer ploughing, as they have been advising, they could have minimized the loss. Rain destroyed onions on about 12 500 acres [about 5059 ha] out of the 20 000 acres [about 8094 ha] in the district, [they] said. The government has sanctioned compensation to

8729 onion farmers. Enumeration of damage is going on.

[byline: D Vincent Arockiaraj]

communicated by: ProMED-mail <promed@promedmail.org>

[A large number of fungal, bacterial, and nematode pathogens, as well as several viruses and phytoplasmas, are known to affect onion (_Allium cepa_) and related crops. It is not clear which root rot is referred to above. Generally, most root rots of the crop are likely to be due to soilborne bacteria or fungi (for example, _Pythium_, _Rhizoctonia_, _Fusarium_ spp.). Most root rot pathogens are soilborne and favoured by humid conditions.

The anthracnose-twister disease complex (ATDC) mentioned above is caused by fungi including _Glomerella_, _Colletotrichum_, and _Gibberella_ species. Severe crop losses of up to 100 per cent have been reported due to ATDC. Spread occurs mainly with infected plant material and by mechanical means. Disease management may include removal of infected crop debris to reduce inoculum, crop rotation, fungicides (although effectiveness may be limited), biocontrol organisms (for example _Trichoderma_ species), and cultural measures (reduction of moisture in the crop).

Some of these measures have been recommended above and are likely to be helpful for management of root rot problems, but reliable diagnosis of the specific pathogen(s) involved is required for designing effective management strategies for the local situation.

Maps

India (with states):

<https://url.emailprotection.link/?bxhKZvLU0Jrpg6QSYMLjDNxcR5ZiODlywjhtDTYBuV09BWjFABuc2Ofa0yVKxvbFaDKaK6JZXs0h0uM-sZc86QR_0oFROTmXyVRSXd78yOJVnKnSTCrdt-F02JA0TgSHq> and <https://url.emailprotection.link/?b05QFwqPTij9Or0JNntK2Ta028HK0Hy9cXDrxF4Qezb0M45_70-mD-E6Jw6k28UsgiT5sQ8Yjt0o7WMCuXCXBHw~~>

Tamil Nadu districts:

<https://url.emailprotection.link/?bw9yxUIb5oy9l_krq09LVpNMsNlKneucHvVKUyqP99kuIop6bA0GVRAOUw_Swr872tIZoPJF2pFoXQhUgspMw7XZCpGSzOE8sUJW5DHEpNi0ANLzMVHaAnNj-AyVb-LOZ>

Pictures

Photo gallery of some onion diseases:

<https://url.emailprotection.link/?bhI-e0VKwbs04OZR4z79TxFWh0oKq7ejDek-K6bh5VJdhGuvqHIvYSlN0fAtjvB3qCWy1giEkIWEXjSYg9sH7_g10hidtPQL4Ub297B5PZmpEcqpkdclfNGi6R5s8XnbW>

ATDC symptoms on onion:

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<https://url.emailprotection.link/?bcVCiJKzSO-2hA3A_ALle2O1BsT44O3GR0moEEWsp90XyQNaWj-XpX8WmnyhI5NaNWOpw-P5Wtwdqb7g8tkwxhHDcvBz0eymJ7OCz5TM3IPQYdw8UfHkCF_I2f5tWXofhMGoIQwyAbhwkj_pj0N-V4F5HCDoVfJrQd0eGY3iYJj0~>

and