Study on the Reaction of Sugarcane Genotypes (CIRAD-2011) to Sugarcane Smut (Sporisorium scitamineum) in the Ethiopian Sugarcane Plantations

Sugarcane smut is caused by Sporisorium scitamineum, a basidiomycetous fungus that exists in several physiologic races [1,2]. It is believed to be originated in Asia and spread slowly to other continents through Africa in the late nineteenth and early twentieth [3]. S. scitamineum is one of the most prevalent diseases and it has been responsible for the demise of several leading varieties [4-6]. This disease was first reported in Ethiopia with the commencement of commercial sugarcane plantation at Wonji Shoa in the early 1950’s [7]. Since then, it spreads to other newer sugarcane commercial farms and is threatening the sugar industry due to its effect on cane yields.

Symptoms of sugarcane smut include black whip-like structures from terminal meristem or meristems of lateral buds of infected stalks [8]. On maturity, the whip raptures and frees millions of tiny black spores which are then disseminated by wind. Other symptoms include smutted side shoots, stem galls, grassy stools, bud proliferation, general reduction in plant size, and increased tillering [1,9,10]. Perpetuation of the smut pathogen occurs through planting diseased seed cane. In plant cane, smut infection usually remains latent in the buds of underground stubble. When such buds are harvested, the shoots that come up bear smutted whips [1]. Primary transmission of the smut fungus occurs through planting diseased seed cane. Secondary spread is through windblown spores. Spores in or on soil are carried to different fields by rain or irrigation water where they can cause new infections to cane [1].

Smut reduces the yield and quality of sugarcane. Reduction in yield and quality varies widely in different sugarcane growing areas of the world and is mainly dependent on the races of the pathogen present, the sugarcane genotypes and the prevailing environmental conditions [11]. Estimates of economic losses have ranged from negligible to levels serious enough to threaten the agricultural economy of an area [11].

Sandhu et al. [4] was reported, sugar cane smut can cause 12%–75% yield losses. Lee Lovick [11], was also mentioned, a total crop failure may possible if susceptible genotypes are used and conditions are favorable for infection. In Ethiopia sugarcane smut causes 19.3 to 43% in sugar yield and 30 to 43% in cane yield [12], the total monetary loss due to this disease in the older sugar estates of Ethiopia was estimated to about ten million birr per year [13]. According to Firehun et al. [13] Smut in Ethiopia led to the discontinued cultivation of varieties like Co 419 and NCo 310.

The most efficient and economic method for disease control, including sugarcane smut, is the use of resistant varieties [14-16]. The efforts made by the Research and Training of Ethiopian Sugar Corporation to attain high-yielding, disease-resistant Saccharum spp. which can be introduced for commercial production and to introduce Saccharum spp. hybrid clones with particular attributes for breeding program results with continuous use of introduced germplasm mainly from CIRAD and other organizations and institutes abroad. About 165 genotypes in four batches have been imported from CIRAD during 2011 – 2015. After the quarantine precautions are being exercised in closed quarantine at Worer center of EIAR [Ethiopian Institute of Agricultural Research], 31 genotypes from the first batch [CIRAD 2011] have evaluated for their reaction to smut at Metehara Sugarcane Plantation Farm.

To evaluate the reaction of sugarcane genotypes [CIRAD-2011] to sugarcane smut

Study on reaction of the newly imported genotypes to sugarcane smut was conducted in Metahara sugarcane plantation during 2014/15 cropping seasons. From the test genotypes, stalks were cut from 10 month-old seed cane nursery. The leaves were detached from the stalks to expose buds and then cut into single-budded setts. To swell up the buds and ensure their susceptibility, the tested materials were incubated for an overnight in a polythene bag filled with a liter of water following the procedures of Bock [17].

Sugarcane smut spore were collected from infected fields of Metehara sugarcane plantation commercial farm, and its viability were tested before it was used for inoculation. The incubated setts were immersed in the spore suspension [5 x 10⁶ spores ml-¹] for 30 minutes (Lee-Lovick, 1978). To create favorable condition for infection, the inoculated setts were again incubated in a polythene bag filled with a liter of water just after inoculation [17].

A day after inoculation, the planting material were planted in Randomized Complete Block Design [RCBD] with three replications in the field number “OR 19C of Metehara Sugarcane Plantation”. Plot size was six furrows of 6 m length each, i.e. 52.2 m². In the course of the experiment, all cultural practices remain the same as recommended for commercial sugarcane production.

During the course of the experiment, data on smuted stool count/ observation begins six weeks after planting and continues at 10-day intervals till ten months after planting. Total number of stool count was taken at four months after planting. After recording smut-affected stools, they were uprooted and buried at the edge of the field. Then, evaluation of genotypes for resistance to smut was made based on percentage of infected stools by adopting the scale used by Latiza et al [18] (Table 1).

Table 1: Disease rating scale [18].

A total of 32, thirty one genotypes of CIRAD 2011 and one widely grown commercial check cultivar, which were planted during 2014, had shown variable reaction to sugarcane smut isolates at Metehara Commercial sugarcane plantation farm. Among these, no any material was shown an immune reaction to the Ethiopian sugarcane smut isolates. While about 81.3% of the tested materials have shown from moderately resistant to very highly resistant reaction in which 21.9%, 9.4%, 21.9% and 28.1% were Very Highly Resistant (VHR), Highly Resistant (HR), Resistant (R) and Moderately Resistant (MR) reactions to sugarcane smut respectively. Genotypes like FG 06 729, FG 03 526 and FG 03 173 which have imported to the country with import certificate information of resistant reaction to sugarcane smut have found to be very highly susceptible to the Ethiopian sugarcane smut isolates (Table 2). Likewise genotypes PSR 97 051 (intermediate), FG 02 551 (susceptible) and FG 03 396 (susceptible) had brought to the country with moderately resistant, intermediate and resistant reactions information respectively. Different sugarcane cultivars in the world may react differently to sugarcane smut isolates. For example cultivar H50-7209 is susceptible to smut in South Africa, but resistant in Taiwan [19]. NCo376 which has been considered as resistant cultivar in China [20], is out of production due to its high susceptibility to sugarcane smut in the Ethiopian Sugarcane plantation [13]. Unlike the varietal reaction information in the import certificate, this study has shown that about 16.1% of the test genotypes have not competently resist to the Ethiopian sugarcane smut isolates. In general, 18.7% of the tested materials in this study were shown intermediate (3.1%), susceptible (6.25%) and very highly susceptible (9.4%) reaction (Table 2) so that these genotypes will not be considered as promising genotypes which can competently resist to sugarcane smut in the country.

Table 2: Reaction of CIRAD 2011 genotypes to Smut.

Thirty one genotypes of CIRAD 2011 and one widely grown commercial check cultivar, a total of 32 genotypes, which were planted during 2014, had shown variable reaction to sugarcane smut. Among these, no any material was shown an immune reaction to the Ethiopian sugarcane smut isolates. While about 81.3% of the tested materials have shown from moderately resistant to very highly resistant reaction in which 21.9%, 9.4%, 21.9% and 28.1% were very highly resistant (VHR), highly resistant (HR), resistant (R) and moderately resistant (MR) reactions to sugarcane smut respectively. 18.7% of genotypes were shown intermediate (PSR 97 051), susceptible (FG 02 551, FG 03 396) and very highly susceptible (FG 06 729, FG 03 173, FG 03 526) reaction, so that these genotypes won’t be considered as promising genotypes which can competently resist to sugarcane smut in the country.