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Mai;:.e Stalk Rot Complexes 295Late wilt has been l)bserveel in Egypt and India (Sabet et 11. 1961; Samra et al. ]962, 1966: Puyaket a/. 1970a; Jain et al. 1975). This disease has not been reported so far from ny other countr'. It isessentially a vascular eli 'case of maize stalk occurring in the tr pic. (Renfro and Ulstrup, 1976). TIlepathogen kills the plants prematurely at the now ring stage. fnfected plants d not show sympt msuntil they reach the tasselling stage and then start wilting from Ule top lcaves. The leaves are at firstdull green, they turn yellow and eventually become dry. The vascular bundles in the stalk arereddish-brown and the nod s also turn to the same colour. [n advanced stages, the lower internodesbecome dry, shrunken and hollow. Frequently, a wet rot develops in the lower part of stems.3. Fusarium stalk rot lFusarilim moniliforme Sheld.= Gibberella monilif()rme (Sheld.)Wineland]Dry or FuariulIl stalk rot of maize caused by species of Fusarium is widely distributedthroughout the world I Koehler, 1960). F. I/lonilijorme is able to cause the premature death of plants(Koehler and Boewe. 1957). It has been proved to be a more virulent pathogen as compared to F.graminearum (Koch and Murwin. 1945). F. lIIonilijorme frequently causes comparatively moredamage in tropical a.~ compared to temperate countries (Cappe lini, 1956; Wernham. 1959: Christensenand Wilcox 'on, 1966). Sometimes. both pathogens affect plants in th same fields, and it is no wonderwhy the two or additional Fusaria have often been confused. This has led to several false reports in thepast, and diagnoses are still confounded (Mace et al., 1981). In India, the disease was first reported inthe Mount Abu area in 1957 and in recent years maize workers have been quite concerned with thisproblem especially in klwrij (rainy) season.. The symptoms become apparent when the crop enters thesenescence phase. Initial symptoms are similar for both pathogens and characterized by reddishdiscolouration in the interior of the stalks. The disease causes a permanent wilting, leaves becomenabby and basal 'talk tissue obtains a pinkish to purple tinge. Some other species of Fusarium foundassociated with . imilar stalk rots are F. oxysporum. F. culmol'll/n, F. poae, F. monifijormesubg!l/tinans, F. avenael/Ill, F. sl/lphurcu/7/, F. aculJ1inatl/m, F. rosel/m. F. merismoides , F. nivale andF. solani (Rintelen 1965; Zwatz 1969: Kommedahl et a1.. 1972; Karadzhova 1978; Lal and wivedi.1983). Though, these fungi can cause extensive tissue disintegration in the internodes above the soillevel, none of them has been confirmed so far to induce typical symptoms associated with prematuredrying and post flowering stalk rot of maize.Inoculation Techniques and Rating SystemsFor large scale field inoculation, the tooth-pick method is the most desirable for all thepost-flowering and Pvthiu1I1 stalk rot pathogens, chiefly because of its ease of preparation of theinoculum and f30idity of the inoculation procedure. In this method, only 5-10 seconds are required perinoculation. The most appropriate plant stage for inoculation is between tasselling and pollination(Zschege, 1969). The second internode above the ground is usually the first elongated internode and ismost frequently used. Splitting the sulk open and observing the rot is the most reliable method ofdetermining the amount and extent of stalk rot. The score may be done in different ways, including anumerical scale (Young, 1943; Reece, 1949; Andrew. 1954; Koehler, 1960). One of the most commonmethods is to estimate the percentage of tissue decayed in an internode. Whenever the rot extendsbeyond the internode inoculated. the total rating given is equal to the sum of the disease ratings of theinternodes infected. DeVay et a1. (1957) used a 1-4 index scale for estimating stalk rot. Khan andPaliwal (1979) used 0-5, while Gupta and Renfro (972) used 1-10. The latter two scales are moregeneral in use for the stalk rot in question. The index scale 1-9 (modified version of Payak andSharma. 1975) is in use, which is constructed as follows: 1 = 25% of the inoculated internodediscolonized: 2 = 26-50% of the inoculated internode discolonized; 3 =51-75% of the inoculatedinternode discolonized; 4 = 76-100% of the inoculated internode discolonized; 5 = discolouration ofless than 50% of adjacent internodes; 6 = discolouration of more than 50% of adjacent internOdes; 7 =