Evaluation of varietal response to black sigatoka caused by Mycosphaerella fijiensis Morelet in banana nursery

Transcription

1 International Research Journal of Plant Science (ISSN: ) Vol. 2(10) pp , October, 2011 Available online Copyright 2011 International Research Journals Full length Research Paper Evaluation of varietal response to black sigatoka caused by Mycosphaerella fijiensis Morelet in banana nursery Tarla Divine Nfor, Fontem Dominic Ajong and Langsi Ivo Nuincho Phytopathology Laboratory, Faculty of Agronomy and Agricultural Sciences, University of Dschang, West Cameroon, P.O. Box 208, Dschang. Accepted 18 August, 2011 Banana is one of most important food crops that are consumed worldwide. Seven high yielding and disease-free varieties (Jaffa, Adi, Williams, Gal, Nandi, Asdia and Ofir) were obtained from tissue culture in Du roi (South Africa) and Rahan (Israel) laboratories. The responses of these varieties to black sigatoka caused by Mycosphaerella fijiensis were evaluated in the nursery of C.D.C Ndongo Banana Plantation in Tiko, South West Region of Cameroon. A completely randomized design was used with 12 replicates. Data were collected on leaf emission rate (LER), number of days from unfurling of heart leaf to the formation of streaks (incubation period), number of days from streaks formation to spots formation (latency period), youngest leaf with infections (YLI), youngest leaf with spots (YLS) and percent disease severity at leaf number (LN) 2,3,4,5,6 and 7. The weekly leaf emission rate for banana varieties varied from 1.2 to 1.4 being higher for Adi and Ofir compared to Jaffa and Gal. Adi and Ofir had the longest incubation period of 28 and 25 days, respectively. A significant difference was obtained between varieties for latency period. Youngest leaf with infections (YLI) was obtained at LN 3 for susceptible varieties while Adi and Ofir with LN 4. Youngest leaf with spots (YLS) was obtained at LN 4 for susceptible varieties while for Adi and Ofir it was at LN 5. The highest percent disease severity (42%) was obtained for Gad and Jaffa at LN 7, while the lowest (10%) was obtained for Adi and Ofir at the same period. Two deleafing cycles and weekly incision of necrotic spots of the disease were performed on Jaffa, Gal, Williams, Nandi and Asdia while one deleafing cycle and bi-weekly incision of necrotic spots was done on Adi and Ofir. Implementation of the deleafing technology in the nursery resulted to reduction in ascospore and conidia production. This study suggests that effective deleafing in banana nursery can be an appropriate management method for black sigatoka disease. Keywords: Banana, black sigatoka, cavendish, Mycosphaerella fijiensis, susceptible. INTRODUCTION Banana (Musa spp) is one of the most important food crops that are consumed worldwide. It is produced in all tropical regions. It is a very important staple food crop in the entire Africa (Stover and Simmonds, 1987; Suzanne, 1997). Bananas account for between 12 to 27% of daily calorie intake and the annual consumption per capita is between 100 and 200 kg in Cameroon. Bananas are staple foods that represent major dietary *Corresponding Author t arladn@yahoo.fr ; Tel: sources of carbohydrate fiber, vitamins A, B6 and C and potassium, phosphorus and calcium. Bananas (including plantains and other types of cooking bananas) are important food crop in Cameroon, where it maybe cooked by baking, boiling, roasting or frying. Intensive commercial production is practiced in the Southwest and littoral regions of Cameroon (Tiko, Loum, Njombe and Ekona). The major exporters of fresh banana fruit in Cameroon are Del Monte, Plantation de Haut Penja (PHP) and Société des Bananeraies de Mbome (SBM) and the Cameroon Development Coorporation (CDC). However, banana yields in Cameroon are estimated at

2 300 Int. Res. J. Plant Sci. 7.7 t/ha (FAO, 2011) much lower than that of Israel (46.9 t/ha), South Africa (49.8 t/ha), Costa Rica (55.5 t/ha), Ivory Coast (47.7 t/ha) and Egypt (40.7 t/ha) figures of the same year. Such low yields are caused by growing pests (insects, mites, nematodes, weeds) and diseases (caused by fungi, bacteria, viruses). In tropical agroecologies, three sigatoka leaf diseases have been described on banana: yellow sigatoka (Mycosphaerella musicola Leach), black sigatoka (Mycosphaerella fijiensis Morelet) and eumusae leaf spot (Mycosphaerella eumusae Colla) (Carlier et al., 2000; Jones, 2000; Crous & Mourichon, 2002). Black sigatoka is the most prevalent and severe among the three sigatoka diseases in banana plantations in Cameroon (Foure, 1993). Average yield losses due to black sigatoka are highly significant ranging from 20 to 50%. Under severe conditions, yield losses may be as high as 80% (Hemeng and Banful, 1994). In the nursery, the only control method for black sigatoka is leaf removal (deleafing). Deleafing seems to be ineffective as seedlings are transplanted to field with 2-4 leaves, much lower than the recommended 5-6 leaves with high level of black sigatoka infections. This is because a single deleafing cycle is programmed for the Cavendish banana varieties. Although black sigatoka disease of banana has been known for a half-century, many fundamental aspects of its epidemiology and the identification of the stages of the symptoms are not well understood. The objective of this study was to assess the varietal response of black sigatoka in the nursery. MATERIAL AND METHODS Experiments were carried out from 6 th June to 30 th September 2009, in the Ndongo section of the Cameroon Development Coorporation located in Tiko (latitude 7.37, longitude 12.35, 46 masl), in the South West Region of Cameroon. A completely randomised design was used with 7 varieties with 12 replications. Five Cavendish group varieties used in the trial came from Du Roi laboratory, South Africa (Asdia, Nandi, Ofir, Adi, Williams) and two other Cavendish group varieties came from Rahan laboratory Israel (Gal and Jaffa). Soil and sand were mixed in a 1:2 ratio (weight/weight) and amended with organic manure and fertilizers. Beds (25 x 1.5 m) were constructed and covered with black polyethylene plastic to prevent weed growth. These beds were separated by furrows of 40 cm wide. Plantlets were irrigated by aerial sprinkling. The nursery was shaded with a black net. The parameters measured were leaf emission rate (LER), disease evolution, disease severity, host-parasite interaction and deleafing technology. For LER, the number of leaves was obtained by counting the full healthy leaf present on the plant and counting started from the top downward. The stage of development of the cigar was obtained by observation (Brun, 1962). Plants were observed every 7 days. To assess the disease evolution, crops were exposed to naturally-occurring inocula from plants in the nursery. Observation of the symptom was based on the methods proposed by Granry and Meyer (1972), readapted by Foure (1982) and Cohan et al. (2002). Disease severity (percent of leaf area diseased) was scored weekly with the aid of a modified Stover (Gauhl, 1989) rating scale. The modified Stover rating scale is divided into 6 grades. Five weekly rating, initiated from the first foliar black sigatoka symptoms, observed after the unfurling of the heart leaf were recorded. Host-parasite interaction was recorded weekly with the aid of modified Vakili (Stover, 1972) criteria. The number of days between unfurling of leaves and the appearance of streaks and spots for each variety used in the trial was counted. Five weekly ratings, imitated from the first foliar sigatoka symptoms, observed after the unfurling of the heart leaf were evaluated. To manage black sigatoka, two deleafing cycles and weekly leaf incision of spotted areas were programmed for highly susceptible varieties (Jaffa and Gal). The first deleafing cycle was programmed 25 days after sowing with mostly the lower leaves removed. The lower lea number (LN) 5, 6 and 7 had smaller surface area and were highly attacked. Incision of spotted areas (coalesced spots) was programmed on LN 4 during the first deleafing. The second cycle was programmed 21 days after the first (46 DAS), during which LN 7 was removed and incision of spotted areas was conducted on LN 6. For variety Williams, Asdia and Nandi, two deleafing cycles were programmed, 25 and 65 DAS followed by weekly incision of spotted areas. For moderately resistant varieties (Adi and Ofir), one deleafing cycle and biweekly leaf incision of spotted areas were programmed. Data were subjected to analysis of variance (ANOVA) using GenStat statistical package. Means were separated using Duncan s New Multiple Range Test at p = Leaf emission rate was analysed using the biological warning method. RESULTS AND DISCUSSION Incubation period A significant difference (P= 0.05) was obtained for incubation period. This means that the time from natural inoculation of plants in the nursery to the appearance of the first symptoms differs among the triploid dessert banana varieties. The incubation period varied between 21 to 28 days. Observations in the nursery showed that streaks appeared on average 21 days for susceptible plants (Gal, Jaffa and Williams) and 28 days for resistant variety (Adi) after unfurling of the heart leaf (Table 1). In similar trial, Stover (1972) reported that the time from the unfurling of the heart leaf to streaks formation varied from 30 days for susceptible plants to 42 days for moderately resistant variety. The cause of this early appearance of streaks was associated to high humidity due to black net

3 Nfor et al. 301 Table 1. Incubation period, latency period, young lea with spot and streak for Cavendish banana varieties Variety Incubation period (days) Latency period (days) Youngest leaf with streak Younget leaf with spots Adi 28 a * 12.3 a * 4 a * 5 a * Ofir 25 a 11.3 a 4 a 5 a Asdia 24 b 10.3 a 3 b 4 b Nandi 24 b 9.3 b 3 b 4 b Gal 21 c 9.0 b 3 b 4 b Jaffa 21 c 8.6 b 3 b 4 b Williams 21 c 8.3 b 1 b 4 b * Means followed by the same letter within a column are not significantly different according to Duncan s New Multiple Range Test (P = 0.05). shading and frequent overhead irrigation by misting. When leaves were thoroughly wetted, ascospores discharge occurred faster. Germination and infection were high on young plants under shade, since humidity was always near saturation (Stover, 1972). Therefore, the time for the formation of appressoria and penetration of stoma by hyphae was longer on the leaves of Adi and Ofir than on Gal, Jaffa, and Williams. Latency period ANOVA for latency period revealed a significant difference (P = 0.05) for banana varieties. Latent periods varied from 8.3 days for Jaffa variety to 12.3 days for Ofir variety. Study in the nursery showed that scattered single streaks appeared at the same time as clumps of streaks on the same leaf of Jaffa, Gal Williams, and Nandi varieties. Necrosis appeared 5 days sooner on Jaffa than on Ofir because of a massive invasion of the tissue. Adi and Ofir had longer incubation and latent periods than Jaffa, Gal, Asdia, Williams and Nandi varieties. This could be explained by the fact that as resistance increased, the incubation and latent periods increased. Also, many lesions did not develop into mature spots and those spots that did appeared had fewer ascospores and conidia. In the nursery, the time from the streaks to necrosis lesions differs according to the level of host susceptibility from 29.3 to 30 days for susceptible varieties (Gal, Jaffa and Williams) and from 37.3 to 39.3 days for resistant (Adi and Ofir) variety. Abedie et al., (2008) reported that the time from the streaks to necrosis lesions varied from 30 days for susceptible variety to days for moderately resistant variety. Youngest leaf with streaks A significant difference (P = 0.05) was obtained for youngest leaf with streaks. This means that the LN on the plants (counting from the top), with streaks was not the same for the varieties. The youngest leaf with streaks was observed at LN 3 on Asdia, Gal, Jaffa, Nandi, Williams varieties, whereas the youngest leaf with streaks was observed at LN 4 on Adi and Ofir (Table 5). One of the factors influencing incubation time was intensity of infection (Brun, 1963). High amount of inoculums were present on the heart leaf and the first leaf of Jaffa, Gal, Williams, Asdia and Nandi which increased the chances for rapid, successful leaf invasions. Youngest leaf with spots There was a significant difference (P = 0.05) for youngest leaf with stage five symptoms. This means that the length of time required for the productions of ascospore and conidia were not the same for all the varieties. The youngest leaf with stage five symptoms was observed at LN 4 on Asdia, Gal, Jaffa, Nandi, Williams, plants, whereas the youngest leaf with stage four symptoms was observed at LN 5 Adi and Ofir plants. Disease severity. Black sigatoka disease severity increase over time. This could be associated to the absence of protective and curative mode of action of fungicides for plants in the nursery. The highest percent disease severity was obtained on the leaves of Gal and Jaffa (42%) at LN 7, while Adi and Ofir had leaves with 10% disease severity at LN 7 (Table 2). This can be explained by the fact that there is a good correlation between the length of time it takes for spots to appear and the amount of spotting. The rate at which the percent disease increases in Adi and Ofir (resistant varieties) is lower than for Jaffa and Gal (susceptible varieties) (Figure 1). This is type of plant resistance is known as horizontal or rate-reducing resistance (resistance that reduces the rate of epidemic development) because, the younger the leaf on which spots appeared, the more spots were developed. When spots were slow to develop and appeared on leaves number 5 or older than number 5, much less spotting developed than when outbreaks

4 302 Int. Res. J. Plant Sci. Table 2. Percent black sigatoka disease severity for Cavendish banana varieties Week LN Jaffa Williams Adi Gal Ofir Asdia Nandi Figure 1. Phases of black sigatoka disease development on the leaves of Jaffa, Gal, Williams, Asdia, Nandi, Adi and Ofir varieties. occurred on LN 4. Thus, when incubation and reproduction time (time from infection to sporulation) were retarded, conditions were not favourable for infections. Black sigatoka disease infected banana leaves at apices and edges more than the centre of the leaf blade. This is because water droplets stand on these positions for a longer period compared to the centre and that ascospores were responsible for the disease. Also more stages of symptom were found on the under surface of the leaf. This could be explained by the fact that the under surface of the leaf contains more stomata than upper surface and infections were much more common on the former (Stover, 1972). Leaf emission rate (LER) and disease evolution The calculated weekly LER values varied from 1.25 to 1.35 for Jaffa, Williams, Gal and Asdia. This corresponds to the real LER value 1.2. This means that, after seven days a new leaf was emitted and the stage of development of the heart leaf was 0.2. The calculated weekly LER values varied from 1.35 to 1.48 for Adi, Ofir and Nandi, corresponding to the real LER of 1.4. This implies a new leaf was emitted after seven days and the stage of development of the heart leaf was 0.4 (Table 3). The period for symptom to change to from stage 2 to necrotic stage is known as the rate of disease evolution and the infestation level is considered as the state of evolution of disease (Foure & Moreau, 1992). The minimum duration for the evolution of symptom from stage 2 to necrotic stage varied from 10.3 to 12.3 days for resistant varieties. Consequently, the rate of disease evolution was higher for susceptible varieties than resistant varieties. The number of symptom types varied from 23 to 32 for highly susceptible variety (Jaffa, Gal and Williams) and from 6.7 to 8.4 symptom types for Adi, Ofir, Nandi and Asdia varieties. Consequently, infestation levels were higher for highly susceptible varieties compared to resistant varieties.

5 Nfor et al. 303 Table 3. Weekly leaf emission rate (LER) and disease evolution of banana varieties. Weeks after planting Number of leaves emitted Leaf emission rate Sum of symptoms Jaffa Williams Adi Gal Ofir Asdia Nandi State of evolution of the disease The youngest leaf with streaks (YLI) was LN 3 for varieties Jaffa, Williams, Gal, Asdia and Nandi, and LN 4 for varieties Adi and Ofir. The youngest leaf with spots (YLS) were LN 4 for varieties Jaffa, Williams, Gal, Asdia and Nandi, and LN 5 for varieties Adi and Ofir. The percent YLI and YLS were 100 % all the Cavendish group varieties. CONCLUSIONS AND RECOMMENDATION The incubation periods for black sigatoka disease were 25 to 28 days for varieties Adi and Ofir, 24 days for varieties Asdia and Nandi, 21 days for varieties Gal Jaffa and Williams. The latent periods for black sigatoka disease were 10.3 to 12.3 days for varieties Asdia, Adi and Ofir, days for Jaffa, Gal, Williams and Nandi. Percent disease severity was 42% for varieties Gal and Jaffa, 24% for varieties Williams, Nandi and Asdia, 10% for varieties Adi and Ofir at LN 7. The weekly leaf emission rate for banana varieties varied from 1.2 to 1.4, being higher for resistant varieties, compared to susceptible varieties. Banana varieties were classified in three groups: resistant varieties were Adi and Ofir; moderately resistant varieties were Nandi, Asdia and Williams while susceptible varieties were Gal and Jaffa. Implementation of the deleafing technology in the nursery resulted to reduction in ascospore and conidia production. Trials could also be carried out to evaluate the response of banana varieties to black sigatoka under field conditions. Other Cavendish banana varieties should be evaluated.

6 304 Int. Res. J. Plant Sci. REFERENCE Abedie C, Carlier J, Mourichon X (2008). Artificial Inoculation on Plants and Banana Leaf Pieces with Mycosphaerella fijiensis responsible for sigatoka Leaf Spot Diseases. Fruits 63 (5): Brun J (1963). La Cercosporiose du Bananier en Guinnee. Etude de la phase ascosporedu Mycosphaerella musicola Leach. These, Institut Français de Recherches Fruitieres Outre Mer, Paris. 196 p. Carlier J, Zapater MF, Lapeyre F, Jons DR, Mourichon X (2000). Septoria Leaf Spot of Banana: A newly discovered Disease caused by M. eumusae (Anamorph Septoria eumusae). Phytopathology 90: Crous PW, Mourichon X (2002). M. eumusae and its anamorph Pseudocrcospora eumusae causal agent of eumusae leaf spot disease of banana. Sydowia 54: FAO (Food and Agricultural Organisation of the United Nations) (2011). FAO Statistics. site accessed july 2011 Foure E (1982). Les Cercosporioses des Bananiers et leurs Traitements Comportement des variétés. Etude de la sensibilité variétale des bananiers t plantains a Mycosphaerella fijiensis Morelet au Gabon (Maladie des Raies Noires) incubation et évolution de la maladie. Fruits 37 (12) : Foure E, Moreau A (1992). Contribution a l etude de la Cercosporiose Noire dans la Zone Bananiere du Moungo du cameroun de 1987 a Fruits 38 (1) : 3-20 Stover RH, Simmonds NW (1987). Bananas. Tropical Agricultural series. Longman Scientific and Technical, UK. 468 pp. Hemeng OM, Banful B (1994). Plantain Development Project. Government of Ghana and International Development Research Centre, Canada. Final Technical Reprot, Suzanne S (1997). Uses of Musa. Pp in: INIBAP Annual Report INIBAP Montpellier France