Sugarcane red rot Colletotrichum falcatum Photo: Ram Naresh · Pexels License · source ↗

Sugarcane red rot (Colletotrichum falcatum)

Red rot, caused by Colletotrichum falcatum Went (teleomorph Glomerella tucumanensis), is the single most destructive disease of Indian sugarcane and has been called the "cancer of sugarcane" since the 1939 epiphytotic that wiped out the variety Co 213 across UP and Bihar. Co 0238, which dominates 80% of subtropical India, was field-tolerant when released in 2009 but has progressively broken down to the CF08 (Pathotype 14) lineage from 2017 onward, with severe outbreaks in 2019-2021 in UP, Bihar and Uttarakhand.

Pathogen identification

C. falcatum is a hemibiotrophic ascomycete that infects through wounds, leaf scars, growth cracks and bud sheaths. Acervuli on infected canes produce hyaline, falcate (sickle-shaped) conidia 16-48 x 4-8 microns with a single oil droplet. ICAR-IISR Lucknow has characterised 14 pathotypes (CF01-CF14) based on differential interactions with a standard host set; CF08 and CF09 are the dominant aggressive pathotypes in current epidemics.

Symptoms

Field symptoms: reddening and drying of the third or fourth leaf from top; entire shoots wilt; canes hollow when split longitudinally
Diagnostic internal symptom: split-open cane shows reddish discolouration of vascular tissue interspersed with white cross-bands — the white-band pattern is the field diagnostic that distinguishes red rot from other discolourations
Smell: infected canes emit a sour, vinegary or alcoholic smell from accumulated fermentation products
Late symptom: shrivelled, hollow canes; rind develops dark red blotches and lengthwise cracks

Hosts and lifecycle

C. falcatum is essentially confined to Saccharum species. Primary inoculum survives in infected seed cane setts and crop debris between seasons. Secondary spread is by rain-splash conidia and through ratoon stubble carrying systemic infection. Setts harvested from infected mother fields are the single biggest amplification mechanism; this is why hot-air or moist-heat seed therapy is recommended before planting. Soil-borne survival is short (1-2 months).

Economic impact

Red rot caused total crop loss in UP and Bihar in 2019-2021 in Co 0238 monoculture blocks — individual farmer losses of Rs 80,000-1,50,000 per hectare. At mill scale, red rot reduces juice sucrose by 30-70%, raises reducing sugars (which prevent crystallisation) and forces mills to reject cane or cut payment rates, breaking the FRP economics for the farmer (see sugarcane-frp-fair-remunerative-price).

Management

ICAR-IISR Lucknow and SBI Coimbatore integrated package:

Resistant varieties as the cornerstone — rotate Co 0238 with Co 15023, Co 0118, Co 98014, CoLk 14201, CoLk 09204 on red-rot-affected blocks; AICRP-Sugarcane releases an annual disease-rating list
Healthy seed: use only nucleus or breeder seed from disease-free mother plots; reject canes with any internal discolouration
Heat therapy: moist hot-air treatment at 54 deg C for 4 hours, or aerated steam at 50 deg C for 1 hour, eliminates systemic infection from setts
Seed dip: carbendazim 0.1% for 10 minutes before planting; can be combined with Trichoderma harzianum 2-5 g/L
Cultural: avoid ratooning red-rot-affected plantings; uproot and burn affected clumps; improve drainage; do not plant cane after cane on infected fields for at least 2 years
Field sanitation: trash burning is no longer recommended; instead chop infected debris and compost separately with Trichoderma-fortified consortia
Chemical control: in mid-season outbreaks, soil drench with carbendazim 0.1% around affected clumps; otherwise systemic fungicides give poor field response once the disease is established

Sources

Red rot of sugarcane - research bulletins. ICAR-Indian Institute of Sugarcane Research, Lucknow.
Sugarcane red rot pathotypes - crop protection notes. ICAR-Sugarcane Breeding Institute, Coimbatore.
Disease screening protocols. AICRP on Sugarcane.