Screening for bacterial stalk rot resistance in corn
--Kalia, V; Basandrai, AK; Singh, A

Bacterial stalk rot of maize caused by Erwinia chrysanthemi pv. zeae is a soft rot appearing at tasseling initiation stage leading to partial to complete death of the plant. This disease is a major problem in sub-tropical areas in low hills and valleys of the outer Himalayas where maize is predominantly grown during the wet season. The disease is reported to cause yield losses up to 85 percent (Lal et al., Ind. Phytol. 23:156-157, 1970). A temperature of 30-35 C and a relative humidity of 90 percent were found to be necessary for maximum disease development (Thind and Payak, Phytol. Medit. 17:59-63, 1978; Saxena, Ph.D. thesis, 1982). Thus, hot and humid conditions favour the disease incidence.

No definite sources of resistance against bacterial stalk rot are known within corn (Zea mays L.) although Sharma, Payak and Sachan (MNL65:111, 1995) reported resistance in allied genera of Trilobachne, Chionachne and wild Coix-25. The present studies were conducted to find out the sources of resistance within maize, and 111 inbred lines were screened under artificial inoculation during the wet season of 1995 at Regional Research Station, Dhaulakuan, Himachal Pradesh, India, which is a known hot spot for the disease. Inoculation was carried out using the syringe method, injecting 2 ml of freshly prepared bacterial cell suspension in the 2nd internode from the ground of each plant at pre-tasseling stage. Incidence was recorded after 25 days of inoculation. Of 111 inbreds, four (DK-3, DK-9, CM-119, 94067) were immune (Table 1) while one (DKI-9304) gave highly resistant reaction (<10 percent). Fourteen inbreds were found to be resistant (10-30 percent), while the remaining were susceptible (44 inbreds) to highly susceptible (48 inbreds). Inbred lines showing immune and highly resistant reactions will be subjected to further genetic studies and used in breeding.

Contribution of inbred lines by various centres of All India Co-ordinated Maize Improvement Project is gratefully acknowledged.

Table 1. Incidence of bacterial stalk rot in different inbred lines of corn.
 

Reaction	Percent incidence	Number of inbreds	Pedigree
Immune	0	4	DK-3, DK-9, CM-119, 94067
Highly resistant	<10%	1	DKI-9304
Resistant	10-30%	14	DKI-9418, DKI-9321, DKI-9505, DKI-9536, DKI-9412, DKI-9401, CM-209, CM-300, CM-210, L21, Bulb-13-2-1-1, Pool 27 (HGR), Pool 20 (Ht, R), GE-440 (Ht1 Ht2), 94065
Susceptible	31-50%	44	--
Highly susceptible	50%	48	--

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