Groundnut leaf spot is one of the important factors limiting groundnut productivity in Africa particularly in the Democratic Republic of Congo (DR Congo). Early and late leaf spot disease of groundnut caused by Cercos...Groundnut leaf spot is one of the important factors limiting groundnut productivity in Africa particularly in the Democratic Republic of Congo (DR Congo). Early and late leaf spot disease of groundnut caused by Cercospora arachidicola Hori and Cercosporidium personatum (Berk & Curt.) Deighton, respectively, can cause considerable yield losses without fungicide management. The main objectives of this research were to analyze plant and disease developmental cycles. Significant differences were observed among the groundnut varieties evaluated for resistance to the leaf spot disease. The results show that plant development cycle can be divided into three developmental stages. A first stage characterized by a low production of leaves, a second stage with a significant leaf development and finally a third stage with a reduction of leaves. Interestingly, the leaf spot disease cycle was also divided in three stages. The disease stage characterized by the highest level of symptom expression was not associated with the plant phase with the highest emerged leaves. Disease symptoms reached the highest pick only after the phase of intense leaf development. The molecular analysis revealed that all the groundnut varieties analyzed were genetically closely related even though they showed different reactions to the leaf spot disease.展开更多
Cercospora leaf spot is fast turning into a critically important disease in Zimbabwe.The disease is caused by Cercospora coffeicola which significantly reduces productivity and quality of coffee.Disturbingly,optimum s...Cercospora leaf spot is fast turning into a critically important disease in Zimbabwe.The disease is caused by Cercospora coffeicola which significantly reduces productivity and quality of coffee.Disturbingly,optimum sporulation of Cercospora coffeicola in culture remains a limiting factor for microbial analysis and quantitative studies of Cercospora leaf spot.Faced with this challenge,an in-vitro study was conducted at Coffee Research Institute,Manicaland,Zimbabwe to examine growth of Cercospora coffeicola in different nutrient media and to determine the best media for Cercospora coffeicola analysis.Six nutrient media were assessed(corn meal agar,oat meal agar,Czapek Dox agar,malt extract agar,yeast extract agar and potato dextrose agar)for the growth of Cercospora coffeicola.The laboratory-based experiment was duplicated,laid out in a Completely Randomized Design,replicated three times and based on Cercospora coffeicola nutrient inoculation.Data were collected on radial growth,colour and texture of mycelium at 3 and 6 days after inoculation.There were significant differences(p<0.05)in the growth of Cercospora coffeicola in media after 3 and 6 days.Malt extract agar had the greatest radial growth(34 mm and 32 mm)of Cercospora coffeicola for trials 1 and 2 respectively,whilst the least growth was in the oat meal agar(14.2 mm and 15.7 mm)for trials 1 and 2 respectively.There were variations in colour and texture of mycelium with malt extract agar,potato dextrose agar and oat meal agar associated with darker colours and rough texture while smooth white mycelia were found in corn meal agar.After considering all nutrient media,malt extract agar was found to be the best media for the growth of Cercospora coffeicola in-vitro.On the basis of our findings,the authors recommend the use of malt extract agar as the primary media for identification and characterisation of Cercospora coffeicola.展开更多
文摘Groundnut leaf spot is one of the important factors limiting groundnut productivity in Africa particularly in the Democratic Republic of Congo (DR Congo). Early and late leaf spot disease of groundnut caused by Cercospora arachidicola Hori and Cercosporidium personatum (Berk & Curt.) Deighton, respectively, can cause considerable yield losses without fungicide management. The main objectives of this research were to analyze plant and disease developmental cycles. Significant differences were observed among the groundnut varieties evaluated for resistance to the leaf spot disease. The results show that plant development cycle can be divided into three developmental stages. A first stage characterized by a low production of leaves, a second stage with a significant leaf development and finally a third stage with a reduction of leaves. Interestingly, the leaf spot disease cycle was also divided in three stages. The disease stage characterized by the highest level of symptom expression was not associated with the plant phase with the highest emerged leaves. Disease symptoms reached the highest pick only after the phase of intense leaf development. The molecular analysis revealed that all the groundnut varieties analyzed were genetically closely related even though they showed different reactions to the leaf spot disease.
文摘Cercospora leaf spot is fast turning into a critically important disease in Zimbabwe.The disease is caused by Cercospora coffeicola which significantly reduces productivity and quality of coffee.Disturbingly,optimum sporulation of Cercospora coffeicola in culture remains a limiting factor for microbial analysis and quantitative studies of Cercospora leaf spot.Faced with this challenge,an in-vitro study was conducted at Coffee Research Institute,Manicaland,Zimbabwe to examine growth of Cercospora coffeicola in different nutrient media and to determine the best media for Cercospora coffeicola analysis.Six nutrient media were assessed(corn meal agar,oat meal agar,Czapek Dox agar,malt extract agar,yeast extract agar and potato dextrose agar)for the growth of Cercospora coffeicola.The laboratory-based experiment was duplicated,laid out in a Completely Randomized Design,replicated three times and based on Cercospora coffeicola nutrient inoculation.Data were collected on radial growth,colour and texture of mycelium at 3 and 6 days after inoculation.There were significant differences(p<0.05)in the growth of Cercospora coffeicola in media after 3 and 6 days.Malt extract agar had the greatest radial growth(34 mm and 32 mm)of Cercospora coffeicola for trials 1 and 2 respectively,whilst the least growth was in the oat meal agar(14.2 mm and 15.7 mm)for trials 1 and 2 respectively.There were variations in colour and texture of mycelium with malt extract agar,potato dextrose agar and oat meal agar associated with darker colours and rough texture while smooth white mycelia were found in corn meal agar.After considering all nutrient media,malt extract agar was found to be the best media for the growth of Cercospora coffeicola in-vitro.On the basis of our findings,the authors recommend the use of malt extract agar as the primary media for identification and characterisation of Cercospora coffeicola.
