Strain-Typing of Potato Virus Y Isolates from Potato in Nigeria by Infectivity Tests and Elisa

In a survey of potato viruses in Nigeria, five isolates of potato virus Y (PVY) were obtained. Two of these, PVY-BL and PVY-BL2, produced symptoms in indicator plants that resembled those caused by PVYN strains, particularly with their ability to incite systemic veinal necrosis in Samsun tobacco. Two isolates, PVY-BK and PVY-KR, reacted positively in ELISA with polyclonal antibodies prepared against PVY-BL and also shared some pathogenic properties with PVYC and PVYO strain groups. They could, however, not be detected in ELISA using monoclonal antibodies specific for PVYC and PVYO strains, an indication that they may be strains that have not previously been described or are antigenic deviants of existing ones

Strain-Typing of Potato Virus Y Isolates from Potato in Nigeria by Infectivity Tests and Elisa

In a survey of potato viruses in Nigeria, five isolates of potato virus Y (PVY) were obtained. Two of these, PVY-BL and PVY-BL2, produced symptoms in indicator plants that resembled those caused by PVYN strains, particularly with their ability to incite systemic veinal necrosis in Samsun tobacco. Two isolates, PVY-BK and PVY-KR, reacted positively in ELISA with polyclonal antibodies prepared against PVY-BL and also shared some pathogenic properties with PVYC and PVYO strain groups. They could, however, not be detected in ELISA using monoclonal antibodies specific for PVYC and PVYO strains, an indication that they may be strains that have not previously been described or are antigenic deviants of existing ones

Incidence and Distribution of Potato Viruses in Plateau State, Nigeria

Potato farms and backyard holdings in Plateau State were surveyed for potato viruses S,X,Y and leaf roll in 1990-1992. Random and biased field samples as well as leaves from sprouted seed tubers from local markets were tested for the four viruses by the enzyme-linked immunisebent assay (ELISA). The incidence of viruses in the fields in four districts was between 45 and 62%, although it reached 90.9% at Chisu in one occasion. Potato virus X (PVX) was the most prevalent while potato virus Y (PVY) and potato leaf roll virus (PLRV) were the least. Virus incidence in plants sprouting from seed tubers in the screen house was more or less comparable to field incidence. Mixed infections by viruses were common, those containing PVX being the most prevalent. PVY scarcely occurred in mixed infections with potato virus S or PLRV

Incidence, distribution and first identification of citrus tristeza virus by RTPCR in citrus orchards in southWestern Nigeria

In order to ascertain the presence, incidence, and distribution of Citrus tristeza virus (CTV), extensive surveys were conducted in citrus growing areas of south-western Nigeria during 2011-12. A total of 565 citrus trees were sampled in three states. Leaf samples were collected and symptom intensity of the trees was recorded. Symptoms observed included stem pitting, stunting, vein clearing and leaf curling. Nucleic acid extracts from leaves were used to detect CTV by RT-PCR using primers PIN1 and PIN2 directed to the conserved 3’ untranslated region. Results show the presence of CTV in the three states surveyed while symptom severity differed from one location to another. Disease incidence varied from 85.2% in Oyo State to 48.4% in Ogun State. Citrus trees were infected regardless of scionrootstock combinations and the virus was detected in sweet orange (87.0%), tangerine (77.6%), grapefruit (73.8%) and lemon (69.5%). This is the first report of molecular detection of CTV in Nigeria.In order to ascertain the presence, incidence, and distribution of Citrus tristeza virus (CTV), extensive surveys were conducted in citrus growing areas of south-western Nigeria during 2011-12. A total of 565 citrus trees were sampled in three states. Leaf samples were collected and symptom intensity of the trees was recorded. Symptoms observed included stem pitting, stunting, vein clearing and leaf curling. Nucleic acid extracts from leaves were used to detect CTV by RT-PCR using primers PIN1 and PIN2 directed to the conserved 3’ untranslated region. Results show the presence of CTV in the three states surveyed while symptom severity differed from one location to another. Disease incidence varied from 85.2% in Oyo State to 48.4% in Ogun State. Citrus trees were infected regardless of scionrootstock combinations and the virus was detected in sweet orange (87.0%), tangerine (77.6%), grapefruit (73.8%) and lemon (69.5%). This is the first report of molecular detection of CTV in Nigeria

Incidence and Distribution of Potato Viruses in Plateau State, Nigeria

Potato farms and backyard holdings in Plateau State were surveyed for potato viruses S,X,Y and leaf roll in 1990-1992. Random and biased field samples as well as leaves from sprouted seed tubers from local markets were tested for the four viruses by the enzyme-linked immunisebent assay (ELISA). The incidence of viruses in the fields in four districts was between 45 and 62%, although it reached 90.9% at Chisu in one occasion. Potato virus X (PVX) was the most prevalent while potato virus Y (PVY) and potato leaf roll virus (PLRV) were the least. Virus incidence in plants sprouting from seed tubers in the screen house was more or less comparable to field incidence. Mixed infections by viruses were common, those containing PVX being the most prevalent. PVY scarcely occurred in mixed infections with potato virus S or PLRV

The relative resistance of cassava cultivars to African Cassava Mosaic Disease (ACMD) as determined by two methods: ranksum and the area under the disease progress curve

Twenty-five newly bred improved cassava cultivars, twenty-three improved from the International Institute of Tropical Agriculture and two local cultivars were evaluated for their relative resistance to African cassava mosaic begomovirus disease (ACMD) at Ibadan, in an area of high disease pressure representative of the forest/savanna transition zone of Nigeria. These cultivars were exposed to natural infection by the viruliferous whiteflies ( Bemisia tabaci Gennadius) and the Disease Incidence (DI) and index of symptom severity (ISS) were assessed for all clones. Results for the Rank-sum (i.e., sum of ranks for DI and ISS for each cultivar) and the area under the disease progress curve (AUDPC) were used to assess the relative resistance of the cassava clones. Those that showed low Rank-sum and AUDPC values were rated 'moderately resistant (MR)', 'resistant (R)', and 'highly resistant (HR)' to ACMD depending on their respective values and deviation from the mean distribution curve. Clones M94/0121 and 94/0239 were rated HR under the two methods. Clone M94/0583 was rated HR under the AUDPC with a deviation from the mean distribution curve of m 2.00 while it was rated R under the Rank-sum method with a deviation from the mean distribution of m 1.99. Also plants of clones ISU and TMS 30572 were rated highly infection (HS) under both methods. Clone TME-1 was intermediate between Moderately Resistant (MR) and Moderately Resistant (MS) under the AUDPC method with a deviation from the mean distribution of 0.00 but observed to be MS under the Rank-sum method with a deviation of + 0.2. The two methods of evaluation gave similar results as revealed by Spearman rank correlation ( r equals; 0.99, P <0.01). However, the AUDPC method is less cumbersome compared to the Rank-sum method. None of the clones was observed to be immune to the disease

Relationships between coinfection with cowpea aphidborn mosaic and cucumber mosaic viruses and yield of cowpea lines with varying resistance to these viruses

The effect of mixed infection of cowpea aphid-borne mosaic (CAMV) and cucumber mosaic (CMV) viruses on cowpea yield varied with the resistance levels of cowpea lines, since there was a strong interaction between the latter and virus infection types atP ≤ 0.01. In cowpea line TVu 3629, with low resistance to both viruses, mixed infection significantly(P ≤ 0.05) reduced most yield components as compared with single infections and uninoculated controls. However, in line TVu 15656, which is highly resistant to both viruses, the effect of mixed infections was not significantly different from that of single infections or from the control. Between these two extremes were cowpea lines TVu 13683 and TVu 410, which were mildly resistant to CMV and CAMV, respectively; single infections significantly reduced the yield components relative to control, although these were generally not different from mixed infections. CMV, hitherto considered to be not economically important in cowpea in Nigeria, could induce severe yield losses when present in mixed infection with CAMV in cowpea lines with low resistance to both viruses. However, since mixed infection did not affect the yield of the highly doubly-resistant TVu 15656 cowpea line, it may be possible to breed for combined resistance to both viruses

Cassava leaf harvesting as vegetables: a cause of vulnerability of cassava plants to cassava mosaic disease and eventual yield reduction

The consequence of harvesting young leaves of cassava as vegetable on the vulnerability of the crop to cassava mosaic disease (CMD) and on storage root yield was investigated using 30 cassava genotypes planted in IITA fields located in the humid forest (Port Harcourt : Onne), forest-savannah transition (Ibadan), southern guinea savannah (Mokwa) and northern guinea savannah (Zaria) agroecologies in Nigeria. Tender apical leaves and shoots of the cassava genotypes were removed from forty plants per cassava genotype with the same number of plants considered as control. Whitefly infestation, disease incidence (DI) and symptom severity (ISS) of the disease were assessed at monthly interval for six months and also at the ninth month after planting (MAP). Yield reduction due to this treatment was calculated as percentage harvest index (HI). Whitefly population fluctuated throughout the period of observation at all locations with higher population obtained generally for treated plants compared to control plants. Sprouting leaves of some treated genotypes were observed with severe mosaic symptoms, while corresponding control showed no mosaic symptoms. Contrarily, no remarkable difference was observed in Zaria between the mean ISS of treated and control cassava genotypes. There was a highly significant difference (P < 0.01) in DI and ISS among cassava genotypes across all locations. Also, there was a highly significant interaction (P < 0.01) in symptom severity between location (loc) and genotype, genotype and treatment (trt), loc and trt. Interaction between loc, genotypes and trt with regard to DI was highly significant at 2, 3 and 4 MAP, while with ISS, the interaction was highly significant all through the counting period. There was a positive relationship between DI and ISS on plants of genotypes 96/1039 and ISU. The percentage HI (27.4) of treated plants of genotype 95/0166 in Ibadan was remarkably lower than the value obtained for corresponding control (41.9) plants. Also, sharp distinction in% HI of treated (39.5) and control (43.8) ISU was observed in Onne with their respective ISS values as 3.7 and 3.2. Therefore, harvesting tender apical leaves and shoots of cassava as vegetables should be discouraged as it increases the severity of CMD infection in the regenerating shoots of cassava with attendant storage root yield reduction

Restriction of virus movement into axillary buds is an important aspect of resistance in cassava to African cassava mosaic virus

Axillary buds and bark samples of resistant, moderately resistant and susceptible (control) cassava genotypes either naturally infected under field conditions or experimentally inoculated by grafting were indexed for African cassava mosaic virus (ACMV). Virus detection was carried out using enzyme‐linked immunosorbent assay and polymerase chain reactions to determine the distribution of the virus within the plant and elucidate the genotypes response to virus movement. Significantly more bud and bark samples were positive for virus on the susceptible genotype TME 117 than resistant genotypes TMS 30001 and TMS 91/02319, or the moderately resistant genotype TMS 30572. Detectable virus concentration was significantly lower in the buds of moderately resistant and resistant genotypes than the susceptible control. Under field conditions, it was significant that more primary stem buds were infected than the buds of secondary and tertiary stems but such a gradient was not obvious with bark samples. Shoots that had asymptomic new leaves after the initial symptomatic leaves had no virus in their buds, but some of the bark samples from the same plants tested positive. A significant interaction was observed between year and stem type, and among year, genotype and stem type with respect to virus detection in bud and bark samples. Restriction of virus movement into axillary buds occurred in all the resistant and moderately resistant genotypes. This may explain ACMV‐infected stem cuttings of resistant genotypes producing healthy plants in subsequent generation