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Plantwise Technical Factsheet

stem rot (Magnaporthe salvinii)

Host plants / species affected
Echinochloa colona (junglerice)
Oryza sativa (rice)
turfgrasses
Zizania aquatica (annual wildrice)
Zizaniopsis miliacea (giant cutgrass)
List of symptoms/signs
Inflorescence  -  discoloration panicle
Inflorescence  -  lesions on glumes
Leaves  -  fungal growth
Leaves  -  necrotic areas
Leaves  -  rot
Seeds  -  lesions on seeds
Seeds  -  rot
Stems  -  discoloration of bark
Stems  -  mould growth on lesion
Stems  -  mycelium present
Symptoms
Symptoms are usually seen after the tillering stage. The first sign is a small, blackish, irregular lesion on the outer leaf sheath near the water line that was initiated by a sclerotium. The lesion enlarges, penetrates the inner leaf sheath, and finally the leaf sheath is partially or completely rotted. After penetrating the inner leaf sheath, infection reaches the culm, where numerous infection cushions are found on the culm. Brownish-black lesions develop on the culm and one or two internodes of the stem eventually rot and collapse (only the epidermis remains intact), leading to lodging, unfilled panicles, chalky grains or death of the tiller. Dark-greyish mycelium can be seen inside hollow, infected stems, with small, black sclerotia dotted over the inner surface. Sclerotia found in the infected tissues are diagnostic.

Conidia, formed from sclerotia or from infected tissue, become airborne and infect the leaves and panicles at later stages of the crop. Disease intensity increases as the crop approaches maturity, and, in the tropics, where moisture is available after harvest, more sclerotia are formed.
Prevention and control

Introduction

Methods to control stem rot include cultural methods to reduce inoculum in the field or regulate infection, and the use of antagonistic organisms, fungicides and resistant varieties.

Host-Plant Resistance

Using resistant varieties is perhaps the best method of controlling stem rot. For rice, however, there are no highly resistant cultivars, though some do not lodge as badly as many of the popular cultivars. Early varieties show more susceptibility to stem rot than late ones. The following resistant cultivars have already been identified (Ou, 1985; Shahjahan, 1987): Early prolific (USA), Dudshar (Bengal), Hondarawala (Sri Lanka), and Ranay, Elon-elon, Arabon, and Kinaturay (Philippines). Gimbuza and Shinriki strains were reported as resistant in Japan (Goto and Fukatsu, 1954); Colusa was also identified as resistant to stem rot (Krause and Webster, 1973).

Oryza rufipogon, O. nivara, and O. spontanea have been identified as sources of resistance to stem rot in California, USA; they may carry the same gene as cultivated rice (Figoni et al., 1983). In the USA in 1993, 87-Y-550 (P1566666) was released with resistance to stem rot derived from O. rufipogon (Oster, 1992; Tseng and Oster 1994). In Bangladesh, of the 4614 accessions tested by Shahjahan et al. (1986), only 1.55% were resistant, including BG 375-1, BR171-2B8, R382-4-3-2, IR2451-49-6-1, IR4407-119-6-7, IR19661-258, Katar, BR51-263-3/AR10 and Ptb 18. In Cuttack, India, 272 rice accessions were screened against 8 isolates of Sclerotium oryzae and only 5 resistant cultivars were identified: MP234, Caloro, IET5633, ARC12751 and Tadukan (Gangopadhyay and Das, 1983). In Haryana, Chand et al. (1985) identified TCM3 and HAUK12-52-4-2 as resistant to stem rot.

Rice cultivars resistant to three sclerotial fungi (S. oryzae, S. oryzae "var. irregulare" and S. hydrophilum) were BR51-33-1-4, RP2151-166-4-1, RP2151-166-4-4-1, RP2151-175-1, RP2151-192-1, RP2151-192-5, RP2151-221-4-2-4, RP2151-224-4 and CR318-548-7 (Singh and Chand, 1986). Among the scented rices with resistance to stem rot were HKR220, HKR216, HKR219, Pak basmati and RPSC 136 (Singh et al. 1985). Other promising rice cultivars in Haryana, India with resistance to stem rot are IET 9700, IET 9701, IET 10413, IET 10417, IET 10418 and IET 10428 (Sunder et al., 1991).

Chemical Control

Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:


Impact
This fungus mainly causes stem tissue rot, with only the epidermis remaining intact: this interferes in the transport of materials to the grain so that yields decrease. The decay of the culm contributes to lodging. The milling quality is lowered because of partial grain filling and chalkiness of grains when infection occurs at an early stage.

Rice yield losses of 5-80% caused by stem rot have been reported from different countries (Ou, 1985). In the Philippines, losses of 25 to 80% in severely infected areas were reported (Reyes, 1956); and in certain fields in Arkansas, USA, yield loss was 75%, with an average annual loss of 10% (Anon., 1930). In India, Chauhan et al. (1968) reported 18-56% yield losses in cv. Co13 and losses of up to 39% in cv. Chaki 59.

An outbreak of stem rot of rice, caused by M. salvinii, was reported from the Murrumbidgee Irrigation Area of New South Wales, Australia. No yield loss was associated with this outbreak although stem rot can cause lodging and yield loss in other countries. A survey of 125 farms revealed that the disease was present on 28 farms, all confined to the eastern part of the area (Watson and Priest, 1998).

Sharma and Mehrotra (1985) analysed yield losses due to varying degrees of infection at different growth stages. The highest percentage loss per plant was observed at the 20th day after infection (7.0% for cv. Basmati, 57% for cv. Jaya), followed by the 40th day after infection (2-30%) and the 60th day after infection (0-15%). The pattern of quantitative reduction in yield and yield component was similar in four varieties, primarily due to reduction in productive tiller number, and was higher in some varieties than others. Infection occurring at later growth stages did not significantly reduce total grain number per panicle.
Related treatment support
Plantwise Factsheets for Farmers
Cambodia, General Directorate of Agriculture; CABI, 2014, English language
Pakistan, Directorate General Agriculture (Ext. & A. R.); CABI, 2014, English language
Aruna, T.; CABI, 2012, Tamil language
Aruna, T.; CABI, 2012, English language
Pakistan, Directorate General Agriculture (Ext. & A. R.); CABI, 2014, Urdu language
 
Pest Management Decision Guides
Cambodia, General Directorate of Agriculture; CABI, 2015, English language
Khan, Y. S.; Saeed, M.; CABI, 2013, English language
Khan, Y. S.; Saeed, M.; CABI, 2013, Urdu language
CABI; CABI, 2017, Spanish language
CABI; CABI, 2016, English language
 
External factsheets
IRRI Factsheets, International Rice Research Institute (IRRI), English language
University of California IPM Pest Management Guidelines, University of California, 2004, English language
TNAU Agritech Portal Expert System factsheets, Tamil Nadu Agricultural University, 2015, English language
Crop Science Extension & Outreach Factsheets, College of ACES, University of Illinois, Urbana Champaign, USA, English language
Crop Science Extension & Outreach Factsheets, College of ACES, University of Illinois, Urbana Champaign, USA, English language
Video factsheets
Agropedia ICRISAT PPT-Videos, IIT, Kanpur, 2014, English language
Agropedia ICRISAT PPT-Videos, IIT, Kanpur, 2014, English language
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