Abstract: Among two different Saccharum species viz; Saccharum officinarum (varieties/ lines Isd 16, Isd 20, Isd 24, Isd 28, BC4 and Saccharum spontaneum (line S 20) were screened against red rot (Colleotrichum falcatum) disease resistance by artificial inoculation following standard plug method. The varieties /lines were graded as various levels of susceptibility and resistance using a standard disease index. Among the varieties/ lines tested Isd 20 and BC4 have shown completely resistant, variety Isd 24, S20 have shown moderately, Isd 16 susceptible and Isd 28 highly susceptible. These varieties/ lines (Isd 20 and BC4) may be utilized as one of the sources of resistance on the breeding programme of sugarcane to red rot disease.
Introduction
Sugarcane is one of the most important industrial cash crops in Bangladesh. Among many cause diseases play an important role to decrease the yield of sugarcane as well as sugar. So far 39 sugarcane diseases have been recorded in Bangladesh of which red rot (Colleotrichum falcatum) is considered as major one (Rahman et al., 1993). Red rot of sugarcane is mainly seed piece transmissible and largely a systemic disease which has not been controlled through fungicides (Lewin et al., 1976). The increasing vulnerability of the cultivated sugarcane to red rot pathogens has made it essential to incorporate the new sources of resistance in to the sugarcane breeding. The wild species S. spontaneum L. has been sought as genetic source of resistance to several diseases like sereh, pythium root rot, gumming, red rot and mosaic (Abott, 1938). Chona (1954) observed that spontaneum proved to be higher resistant to red rot while the nobles canes were susceptible. The present work was taken to determine the resistance sources among different high yielding varieties and wild species of sugarcane.
Materials and Methods
The experiment was conducted at the Bangladesh Sugarcane Research Institute (BSRI) farm, at BSRI, Ishurdi, Bangladesh during 2000-2002 for two seasons. Among six varieties/ lines viz Isd 16, Isd 20, Isd 24, Isd 28, BC4 and S 20 were tested against red rot by the standard plug method (Chona, 1954). Twenty stalks of eight months old cane of each variety were inoculated with a suspension containing a single cultures of C. falcatum isolates collected from naturally infected sugarcane varieties at BSRI. Two months after inoculation, canes were split open longitudinally and lesion width, occurrence and number of white patches, number of nodes transgressed and conditions of tops were scored. The red rot reaction was measured based on 0-9 scale (Srinivasan and Bhatt, 1961).
Results and Discussions
The data on the incidence of red rot on the various varieties/lines of S. officinarum and S.spontaneum to red rot pathogen are given in Table 1. During the period of 2000 to 2002, out of the six different varieties/ lines Isd 20, Isd 24, BC4 showed resistant to moderately resistant. Among another two varieties Isd 16 and Isd 28 showed susceptible reaction to C.falcatum. S. spontaneum line S 20 found moderately resistant. Rahman (2001) also reported that the BC4 and Isd 20 were found moderately resistant and Isd 24, Isd 28 were highly susceptible and Isd 16 was susceptible during 1999-2001. Abott (1938) reported that found S. spontaneum moderately resistant against red rot. Srinivasan (1956) also reported that different variants of S. spontaneum differ in their resistance to any given disease. In this trial for identifying the diverse sources of red rot disease resistance among different species of sugarcane the light type single isolate culture of red rot pathogen and plug method were used. Singh (1956), Sharma and Achutarama (1977), Rahman (1996) reported that light type of isolates are generally most virulent then other types of red rot pathogen. For successful exploitation of sugarcane genetic resources it is very necessary to careful characterization and evaluation of different varieties/ lines among different species. Roach (1977) also reported that selection of the S. spontaneum parent where the aim of hybridization is to transfer a single specific character e.g. disease resistance from S. spontaneum would appear obviously appropriate. The break down of red rot resistance is primarily attributed due to the appearance of new strains/ pathotypes in the red rot pathogen. Various other workers have also reported variability in red rot pathogen (Chona and Padwick, 1942; Rafay, 1950; Rafay and Singh, 1957).
| Table 1: | Resistance ratings of different sugarcane varieties / lines (Saccharum officinarum and Saccharum spontaneum) to light type isolate of C. falcatum |
| R= Resistant (0.0-2.0); MR= Moderately resistant (2.1-4.0); S= Susceptible (6.1-8.0); HS= Highly susceptible (above 8.0) | |
Different environmental factors (temperature, rainfall, soil moisture) are also responsible for infection of red rot pathogen. In spite of the various methods the introduction of resistant varieties is the best approach. It is confirmed from the present study that different levels of resistance of red rot are available in the different species of sugarcane varieties/lines and Isd 20, BC4 and S 20 may be much more useful than others as donors in breeding program aimed at red rot disease resistance.