Phytophthora Pod Rot Research Articles

Long-Term Preservation of Cultures of Phytophthora Species Causing Black Pod Disease on Cacao

<em>Theobroma cacao</em> L. (cacao) is the main raw material in the production of chocolate which is enjoyed worldwide. One of the most important diseases affecting cacao is Phytophthora pod rot and losses up to 100% have been reported. Significant amount of research work is conducted annually on the pathogen but preserving Phytophthora species in culture to support research is always problematic.

Molecular Characterization of Phytophthora Pod Rot of Cocoa (Theobroma cacao L.) in Southwestern Nigeria

Molecular Characterization of Phytophthora Pod Rot of Cocoa (Theobroma cacao L.) in Southwestern Nigeria

Multivariate analysis of genetic diversity in Phytophthora pod rot resistant exotic cocoa germplasm

The current research work was carried out to evaluate the genetic diversity associated with thirty cocoa accessions resistant to Phytophthora. The cluster analysis and principal component analysis evaluated the genetic variability among the different genotypes. The highest number of genotypes were observed in cluster III (8) when qualitative traits were considered. In quantitative cluster analysis, most of the genotypes were placed in separate clusters due to high variability in the germplasm. Principal component (PC) analysis showed that the first three PCs with more than one Eigen-value contributed to 79.9 per cent of variability for different traits. When qualitative and quantitative characters were considered along with resistant reaction, clusters with genotypes highly resistant to Phytophthora pod rot were observed. Hybridization programme involving these resistant hybrids belonging to diverse clusters will result in high yielding hybrids with ample resistance.

Cocoa Clone Resistance to Phytophthora Pod Rot (PPR) and Cocoa Pod Borer (CPB) in South Sulawesi

This research aimed find out the resistant of some superior cocoa clones to Phytophthora palmivora in South Sulawesi. This research covers several stages ranging from selection and sampling of cocoa clones, pathogen exploration to cocoa clone’s resistant test with various methods that is attaching the cocoa pod part to the healthy cocoa pod, applying P. palmivora suspension to the cocoa surface and sticking P. Palmivora isolates to the healthy cocoa pod section. The results showed that the resistance of cocoa clones to the three inoculation methods showed different areas of spotting on each observation day. The three application methods show that different applications can affect the difference in infection rates in each cocoa pod clone so that the spots that arise from infection can occur in various ways.

Potentials of cocoa pod husk-based compost on Phytophthora pod rot disease suppression, soil fertility, and Theobroma cacao L. growth.

Cocoa black pod disease caused by Phytophthora megakarya and reduced soil fertility are major constraints to cocoa production resulting in high yield losses. In the absence of effective control measures and constraints related to the use of chemical fungicides and fertilizers, there is a need to develop additional and sustainable disease and fertilization management strategies. With the lack of studies related to the use of compost in cocoa cultivation, the present study aims to evaluate the potential of cocoa pod husk (CPH)-based compost as a soil amendment to reduce the severity of cocoa black pod disease and enhance plant growth. In vitro antagonism test showed that compost water extracts (CWE) reduced mycelial growth with inhibition rate reaching 100% associated with microorganisms. Disease score of cocoa plantlets grown on compost-amended soils significantly reduced compared to plantlets grown on non-amended soil (control). All compost rates tested significantly increased populations of actinomycetes and fungi and biological activity in the soil. Compost application increased soil pH and majority of the essential elements but decreased Al content, which is toxic to cocoa growth in acidic soils. Soil application of compost at the dose of 20% (v/v) significantly increased stem length and number of leaves compared to the control. This study shows that CPH-based compost can not only improve soil fertility and cocoa growth but also reduce cocoa black pod disease severity by direct effects on inoculums level in the soil and by inducing resistance in the plant.

EFFECT OF ORGANIC AND INORGANIC AMENDMENTS ON PRODUCTIVITY OF COCOA ON A MARGINAL SOIL IN SULAWESI, INDONESIA

SUMMARYReduced soil fertility and damage from pests and diseases have contributed to a decline in productivity of cocoa (Theobroma cacaoL.) smallholdings in Sulawesi, Indonesia over the last decade. In a trial on a marginal, acidic soil in South Sulawesi, young PBC123 cocoa trees were supplied with compost, mineral fertiliser (NPK fertiliser and urea) or dolomite, alone and in combination. After 20 months, the trees supplied with compost were taller, flowered more profusely and had a five-fold higher dry bean yield than other treatments. Treatments had no impact on incidence of cocoa pod borer, Phytophthora pod rot and vascular streak dieback. All of the trees supplied with compost survived, while the control, mineral-fertiliser- and dolomite-treated trees had a mortality rate of 22–45% and symptoms of interveinal necrosis. Leaf concentrations of N, P and K were within the normal range in all treatments. In the control and mineral fertiliser treatments, leaf concentrations of Ca (0.28–0.30%) and Mg (0.11–0.15%) were deficient, but were higher in trees supplied with compost (0.78–1.21% and 0.26–0.29%, respectively). The Mg/K ratio in soil-exchangeable cations and leaves was increased three-fold by the combined compost/dolomite treatment. Supplying mineral fertiliser alone resulted in 3.3 cmol kg−1exchangeable Al, compared to 2.2 cmol kg−1in control soils. Since 10 kg tree−1year−1compost was supplied, a rate that is not practical on most cocoa smallholder farms, further investigation of cost-effective applications of organic matter in conjunction with appropriate formulations of inorganic fertilisers is recommended.

Analysis of Genotype by Environment Interaction on Cocoa Hybrids (Theobroma cacao L.) Resistance to Phytophthora Pod Rot

Phenomenon of genotype by environment interaction was able to influence the stability performance of cocoa resistance to Phytophthora pod rot (PPR). This research had an objective to evaluate the effect of genotype by environment interaction on resistance of cocoa hybrids to PPR. The tested hybrids were F1 crosses between selected clones of TSH 858, Sulawesi 1, Sulawesi 2, NIC 7, ICS 13, KEE 2 and KW 165. There were 14 tested hybrids and an open pollinated hybrid of ICS 60 x Sca 12 was used as control in multilocation trials at four different agroclimatic locations, namely Jatirono Estate ((highland-wet climate), Kalitelepak Estate (lowland-wet climate), Kaliwining Experimental Station (low land-dry climate) and Sumber Asin Experimental Station (highland-dry climate). Trials were established in the randomized complete block design with four replications. Resistance to PPR were evaluated based on the percentage of infected pod for the years during wet climate of 2010 in Jatirono, Kalitelepak and Kaliwining followed in dry climate of 2011–2015 in Kaliwining and Sumber Asin. Variance of data were analyzed for detecting the effect of genotype by environment interaction (GxE) then visualized with a graph of genotype main effect and genotype by environment interaction (a graph of GGE) biplot. There was consistently no interaction effect between hybrid and location to PPR incidence which was affected by single factor of hybrid, year, location and interaction between year and location. The effect of year indicated yearly change of weather was more important to PPR incidence than location difference. A graph of GGE biplot indicated a stable performance of the tested hybrids among locations.

Yield Performance of Locally Selected Cocoa Clones in North Luwu

Participatory selection in North Luwu District selected some locally cocoa clones, of which MCC 01 and MCC 02 the most promising to be developed as clonal material. This research has objectives to observe the stability performance of yield of these clones that enable be characterized of the potency as the basis for recommendation. Observation were carried out in 35 selected-farms be differentiated according to clone’s type, namely MCC 01, MCC 02 and Sulawesi 01 (control) and the year of planting (age). These farms were establised at the main area of cocoa in North Luwu. The assessed variables were the number of pod, yield components, the resistance to cocoa pod borer (CPB), vascular-streak dieback (VSD) and phytophthora pod rot (PPR). Data were recorded through 20 sampled-trees per farm in the period of April 2013 to April 2014 with monthly basis assessment. Data were analyzed refer to Eberhart &amp; Russel method to perform stability parameters of the yield. The results indicate that these clones stable performing yield potency among plant age. MCC 01 and MCC 02 performed yield potency in amount of 3,682 kg/ha and 3,132 kg/ha respectively higher than Sulawesi 01 of 2,772 kg/ha. Evaluation of the resistance, MCC 01 having moderate resistance to CPB and VSD and resistance to PPR, however MCC 02 having resistance to CPB, VSD and PPR. Referring to the potency thus MCC 01 and MCC 02 were legally recommended as clonal material for farmers, restricted at the agroclimatic area similar to the condition in North Luwu.

Testing local cocoa selections in Sulawesi: (ii) resistance to stem canker and pod rot (black pod) caused by Phytophthora palmivora

Cocoa genotypes, selected locally or obtained from the progeny of hybrid crosses and propagated clonally in two trials in Pinrang and Polman Districts, Sulawesi, were evaluated for resistance to Phytophthora pod rot (Ppr) and stem canker caused by Phytophthora palmivora. In each trial, 10–12 clones, including four common to both sites, were evaluated for infections occurring naturally on the farm or induced by artificial inoculation of stems and attached pods. At each site, incidence and severity of stem canker in the clones were evaluated in the early and late wet season of 2013/2014, while Ppr incidence was determined from the cumulative pod harvest of 2010–2012. Incidence and severity of stem canker in the six-year old trees were highly correlated in both years and were higher in Pinrang than Polman, with marked increases during the wet season occurring in more susceptible genotypes (e.g. 65.6%–90.6% incidence in GeniJ in Pinrang). Although Ppr incidence in all clones increased during wet periods, some clones maintained a lower incidence than others during the two year period of evaluation: for example, between the dry season of 2011 and following wet season average Ppr incidence increased from <5% to 26% in the local clone M06 and <20%–46% in the more susceptible RB. Average lesion size following artificial inoculation was higher in both pods and stems in the Pinrang, than the Polman, trial. Positive correlation between results of artificial pod tests and total field Ppr incidence (including immature and ripe pods) suggest that artificial inoculation of attached pods is a reliable method to evaluate Ppr resistance. Similarly, lesion size in different clones following artificial inoculation of stems was positively correlated with naturally occurring stem canker severity. Inconsistencies between responses to inoculated and naturally occurring P. palmivora were found in some clones, for example, ICCRI04, selected from progeny of a hybrid cross with Sca12, and Geni J, a local farm selection, indicating the importance of confirming artificial resistance tests with evaluations on the farm. While resistance to both diseases was confirmed in some local selections notably M06, M05 and Panimbu Red, no significant correlation occurred in either trial in the responses to stem canker and Ppr (whether naturally occurring or induced artificially by inoculation), suggesting independent resistance mechanisms may operate in stems and pods. Broad-sense heritability estimates, based on clones common to the two trials, were high (0.85 and 0.63 for stem canker incidence and severity, respectively, and 0.41 for Ppr incidence) indicating a strong influence of host genotype on the response to P. palmivora.

Black pod disease on cacao (Theobroma cacao, L) in Ghana: Spread of Phytophthora megakarya and role of economic plants in the disease epidemiology

To implement management strategies of Phytophthora pod rot (black pod) diseases successfully, knowledge of the role of economic plants, and the diversity and distribution of Phytophthora species on these plants in the cacao ecosystem is essential. In this study, the spread of Phytophthora megakarya in the cocoa growing districts of Ghana was monitored through annual surveys from 1985 to 2012. In addition, from July to October, 2008, Phytophthora was isolated from randomly collected non-symptomatic rootlets of economic plants on cacao farms and from symptomatic pods and stems of cacao from 139 locations in 22 districts in the cacao growing regions. A total of 1459 Phytophthora isolates from 22 plant species belonging to 19 families were characterized. The Phytophthora isolates showed six different morphological patterns on Campbell Vegetable Juice Agar medium. The patterns were variable stellate striate, cotton wool-like, deep cotton wool-like only at colony margin, light cotton wool-like pattern only at colony margin, and dense aerial, fluffy colonies without pattern. However, microscopic examination of the sporangia of the isolates revealed only two species, Phytophthora palmivora and P. megakarya. P. megakarya was found to have spread from Akomadan and Bechem in 1985 to 50 more administrative districts in 2012. This study also represents the first report of isolation of P. megakarya from Xanthosoma saggitifolium, Musa paradisiaca, Elaeis guinnensis, Persea americana, Carica papaya, Mangifera indica, Colocasia esculenta, Athyrium nipponicum and Ananas comosus on cacao farms in Ghana. The fact that economic plants on cacao farms harbour Phytophthora species may explain the failure to obtain appreciable control of Phytophthora diseases as the current management of these diseases is mainly targeted at the host crop, Theobroma cacao.

Testing local cocoa selections in three provinces in Sulawesi: (i) Productivity and resistance to cocoa pod borer and Phytophthora pod rot (black pod)

Trials were established on smallholder cocoa farms in three provinces in Sulawesi to assess productivity and constitutive responses of local cocoa clones to cocoa pod borer (CPB) and Phytophthora pod rot (Ppr) in different environmental situations. Twelve clones per trial (local farmer-assisted selections or clones produced by hybridisation programs in East Java and Malaysia) were tested in the districts of Pinrang, Polewali-Mandar and North Kolaka, including four standards common to the trials: the Malaysian clone, PBC123, and three selections from Sulawesi farms. The clones were evaluated from the time they started fruiting in 2010 (about two years after planting) for two years during which time chemical pesticides were not applied. Otherwise farms were managed according to recommended practices, including harvesting each fortnight, fertiliser application and heavy and light pruning, depending on the season. Butter fat content was generally lower than 50% but was higher in three local selections in Pinrang, M04, RB and Panimbu Red. While strongly dependent on genotype, fat and shell content and pod values in the common standards showed some variation between sites. The bean size and fat content of PBC123 was low, but this clone yielded better than most of the clones tested. For the common standards, yield estimates obtained from average yield per tree were higher in Pinrang (735–1100 tons/ha/annum) than in N. Kolaka (342–894 ton/ha/annum) or Polewali-Mandar (485–899 tons/ha/annum) indicating a marked site-effect. The number of flowers produced was higher in the common standards in Pinrang. Soil parameters including pH and exchangeable calcium, magnesium and potassium were higher in Pinrang than in Polman, although both sites were deficient in soil nitrogen and organic carbon. Lower average CPB infestation rates in ripe pods for the two-year evaluation period occurred in Pinrang (48–66%) and Polewali-Mandar (19–68%) than in N. Kolaka (77–80%). In most of the clones, total and severe CPB incidence decreased during the high pod season but some selections, such as M04 and TR01, maintained a low total and severe CPB incidence in both the low and high pod seasons, indicating partial resistance. In the ripe pods of common standards, the highest average Ppr incidence (ranging from 10 to 14%) occurred in N. Kolaka, which had a higher annual rainfall than the other sites. In ripe pods in the Pinrang trial, Geni J, M06 and Panimbu Red had a low Ppr incidence (4.4–4.8%) while M04 was Ppr-susceptible (23%). Incidence of Helopeltis spp. was high in the immature pods of some clones (exceeding 30% of the total harvest in M01 and Geni J in Pinrang). The results show that the performance of clones is affected by the locality in which they are grown, as well as their genotype, indicating the importance of testing clones under different environmental conditions. While the trials confirmed the efficacy of farmer-assisted selection, they also indicated that clones resistant to CPB, were susceptible to Ppr or other pests/diseases, and vice versa. For example, local selection, M04, was highly susceptible to Ppr, yet resistant to CPB. Therefore, the results indicate the importance of efforts to screen the progeny of hybrid crosses that combine resistance and yield traits.

Bahasa Indonesia

The Phytophthora pod rot (PPR) caused by Phytophthora palmivora is one of important diseases affecting the decrease of cacao productivity. The use of endophytic Trichoderma have a big potential for controlling this disease. The rate of PPR incidence in twelve weeks after three times application by spraying of ART-4/G.J.S 09-1559 isolate of Trichoderma asperellum with concentration of 1 g L -1 , 2 g L -1 , 4 g L -1 was 5.4%, 5.3%, and 3.7%, respectively per week; while the rate of PPR incidence on control was 8.4% per week. Apparently healthy pods pretreated with above concentrations of T. asperellum in field showed 30, 0, and 0% infested by PPR on its surface, respectively after one week incubation in laboratory, compared to a 90% of surface infestation by PPR on control. After 12 week of inoculation, T. asperellum was recovered from pod tissue. This data demonstrated the potential of T. asperellum as bio control agent of PPR disease on cacao.

On-Farm Evaluation of Trichoderma asperellum on the Suppression of Phytophthora megakarya Causing Pod Rot of Theobromae cacao in Nigeria

Aims: The study examines the inclusion of biological control hitherto neglected, as part of the IPM strategies in a farmer participatory approach. Study Design: The experimental plots were set up within a completely randomized block experimental design with 3 replicates. Place and Duration of Study: The field trials were carried out in 2009 at Iloro-Idanre, Owode, Khalime and Bendeghe communities in the South -West and South - South of Nigeria. Methodology: The bio-control agents used ( Trichoderma ) was isolated from the leaves of cacao tree and natural forest reserve soils in Ibadan, Nigeria, the culture was stored and maintained in sterile distilled water on small plugs of modified potato dextrose agar. Five Treatments: Funguran OH, Trichoderma , Funguran OH (1) + + Trichoderma (5) times, Funguran OH (2) + Trichoderma (4) and Sterile distilled water were applied. Disease incidence ratings were taken after the each application till the end of the trial. Data were taken on number of pod and cherelles production, while number of damaged and Phytophthora pod rot were taken as total pod loss on each tree in each plot. Results: The pod productions in all the treatments differ significantly from the untreated

English

&nbsp; &nbsp; The level of resistance against&nbsp;Phytophthora&nbsp;pod rot (PPR) was assessed among locally-selected accessions of cacao, the so-called selection of Nkoemvone (SNK), in Cameroon. The evaluation approaches have included four tests: Leaf disc inoculation (LDT); detached pod inoculation (DPT); artificial inoculation of pods and counting of successful infections (%SI); and field observations of the disease incidence (FI). The studied accessions were classified into four groups according to their genetic origin: SNK; SNK600-Tr (SNK*ICS); SNK600-Tr*UA (UPA*ICS); SNK600-Tr*UA (UPA*SNK). In all four testing methods, the groups UPA*ICS and SNK appeared respectively as the least and the most susceptible accession groups. Four resistance classes were defined for each testing method. A great part of the accessions were found in the intermediary resistance classes, based on DPT, LDT and %SI. Few accessions have displayed a significant level of PPR resistance in all testing methods. Rank correlation of the different accessions groups based on their performance in the four tests have shown that all correlation coefficients were positive (r&nbsp;= 0.37 &ndash; 0.87) and significant (p &le; 0.06). The best correlation was registered between %SI and FI with&nbsp;r&nbsp;= 0.87 (p = 0.01). Subsequently, a unique classification of all accessions was done according to the scores recorded in all the testing methods. The use of locally-selected accessions (SNK) in the varietal development as well as in the cacao seed production is discussed. &nbsp; Key words:&nbsp;Cacao plant pathology, oomycetes, screening methods, resistant cultivars, selection. &nbsp

CONTROL OF COCOA POD BORER AND PHYTOPHTHORA POD ROT USING DEGRADABLE PLASTIC POD SLEEVES AND A NEMATODE, Steinernema carpocapsae

&lt;p&gt;Cocoa pod borer (CPB; &lt;em&gt;Conopomorpha cramerella&lt;/em&gt;) and Phytophthora pod rot (PPR; &lt;em&gt;Phytophthora palmivora&lt;/em&gt;) are serious pest and disease on cocoa plantations in Indonesia. Both pest and disease have been controlled with limited success using cultural practices such as pruning, frequent harvesting, sanitation, plastic sleeving, and chemical pesticides. An experiment was conducted on cocoa plantings in Pinrang Regency, South Sulawesi during the wet season of 2008/09 to test the effect of pod sleeving (with transparent degradable and non-degradable plastic bags) and nematode application on CPB and PPR infestation. The nematode, &lt;em&gt;Steinernema carpocapsae &lt;/em&gt;(10,000 active juveniles per pod) was sprayed three times at intervals of 10 and 20 days. Pod damage by CPB was observed at harvest time, while PPR disease incidence was evaluated every week until harvest time. Results showed that all pods in the field were infested by CPB as indicated in control samples. Pod sleeving using both non-degradable and degradable plastics significantly reduced pod damage by CPB, from 62.3% in the control treatment compared to 8.4% in the CPB treatment. A combination of pod sleeving and nematode application had a synergistic reduction of pod damage by CPB resulting in totally healthy pods. Pod sleeving with degradable and non-degradable plastics also reduced pod damage by PPR significantly. Pod sleeving with non-degradable plastic suppressed the disease incidence almost zero until 6 weeks after sleeving and the rate of disease incidence was 3.6% per week. However, with degradable plastic, the disease suppression was even longer (7 weeks after sleeving), indicating that the degradable plastic is more effective. Combination of sleeving and nematode application slightly increased PPR infection. Sleeved pods in general had lower rates of PPR infection compared to pods treated with nematode or untreated pods (control). In these two applications, the rate of disease incidence was 7.8% and 8.3% per week respectively. The study implies that biological control using entomopathogenic &lt;em&gt;S. carpocapsae &lt;/em&gt;and degradable plastic sleeves are effective and environmentally-friendly to control &lt;em&gt;C. cramerella &lt;/em&gt;and &lt;em&gt;P. palmivora

CONTROL OF COCOA POD BORER AND PHYTOPHTHORA POD ROT USING DEGRADABLE PLASTIC POD SLEEVES AND A NEMATODE, Steinernema carpocapsae

&lt;p&gt;Cocoa pod borer (CPB; &lt;em&gt;Conopomorpha cramerella&lt;/em&gt;) and Phytophthora pod rot (PPR; &lt;em&gt;Phytophthora palmivora&lt;/em&gt;) are serious pest and disease on cocoa plantations in Indonesia. Both pest and disease have been controlled with limited success using cultural practices such as pruning, frequent harvesting, sanitation, plastic sleeving, and chemical pesticides. An experiment was conducted on cocoa plantings in Pinrang Regency, South Sulawesi during the wet season of 2008/09 to test the effect of pod sleeving (with transparent degradable and non-degradable plastic bags) and nematode application on CPB and PPR infestation. The nematode, &lt;em&gt;Steinernema carpocapsae &lt;/em&gt;(10,000 active juveniles per pod) was sprayed three times at intervals of 10 and 20 days. Pod damage by CPB was observed at harvest time, while PPR disease incidence was evaluated every week until harvest time. Results showed that all pods in the field were infested by CPB as indicated in control samples. Pod sleeving using both non-degradable and degradable plastics significantly reduced pod damage by CPB, from 62.3% in the control treatment compared to 8.4% in the CPB treatment. A combination of pod sleeving and nematode application had a synergistic reduction of pod damage by CPB resulting in totally healthy pods. Pod sleeving with degradable and non-degradable plastics also reduced pod damage by PPR significantly. Pod sleeving with non-degradable plastic suppressed the disease incidence almost zero until 6 weeks after sleeving and the rate of disease incidence was 3.6% per week. However, with degradable plastic, the disease suppression was even longer (7 weeks after sleeving), indicating that the degradable plastic is more effective. Combination of sleeving and nematode application slightly increased PPR infection. Sleeved pods in general had lower rates of PPR infection compared to pods treated with nematode or untreated pods (control). In these two applications, the rate of disease incidence was 7.8% and 8.3% per week respectively. The study implies that biological control using entomopathogenic &lt;em&gt;S. carpocapsae &lt;/em&gt;and degradable plastic sleeves are effective and environmentally-friendly to control &lt;em&gt;C. cramerella &lt;/em&gt;and &lt;em&gt;P. palmivora

Host Plant Resistance to Phytophthora Pod Rot in Cacao (Theobroma cacao L.): The Role of Epicuticular Wax on Pod and Leaf Surfaces

An article published by Asian Network for Scientific Information; International Journal of Botany 8 (1): 13-21, 2012

A Diagnostic Study of Constraints to Achieving Yield Potentials of Cocoa (Theobroma cacao L.) Varieties and Farm Productivity in Nigeria

Increasing farm productivity is a major breeding objective in crop improvement of any crop species. However, there is usually a gap between yields reported in experimental station and that obtained by farmers. In this study, diagnostic tools of Metaplan, Pair wise ranking, Stakeholders’ analysis and Venn diagram were used within a participatory Focus Group Discussion (FGD) with farmers in the three major cocoa growing States of Nigeria, namely, Ondo, Osun and Cross River States to identify causes of low farm productivity and constraints to cocoa cultivation in Nigeria. Results showed the black pod disease (Phytophthora pod rot), old age of cocoa trees, poor access to improved planting materials, termite infestation and insufficient chemicals as the most important factors responsible for low cocoa yields obtained by farmers. We also found that local buying agents, extension outfits of national agricultural development projects (ADPs) and farmer field schools (FFS) and farmers’ organizations (FOs) were the closest stakeholders to cocoa farmers in the States investigated. This study revealed the need for development of improved cocoa varieties that are resistant to the black pod disease and a functional system of seed distribution to facilitate greater access to improved varieties. We therefore suggest that programmes should be designed to increase farmers’ access to improved planting materials, inputs, finance and involvement in participatory problem-identification and solution strategies development process.

Thickness of the Cocoa Pod Husk and its Moisture Content as Resistance Factors to Phytophthora Pod Rot

Thickness of the Cocoa Pod Husk and its Moisture Content as Resistance Factors to Phytophthora Pod Rot

Selection for resistance to Phytophthora pod rot of cocoa ( Theobroma cacao L.) in Cameroon: Repeatability and reliability of screening tests and field observations

Phytophthora pod rot (Ppr) disease caused by Phytophthora megakarya is the major constraint to cocoa production in Cameroon. The development of resistant varieties requires the use of effective resistance testing methods. The repeatability and reliability of the leaf disc and detached pod tests, as applied in selection activities in Cameroon, were studied. Repeatability of the tests was estimated by calculating the correlation ( r) between resistance scores of clones, progenies and individuals within progenies in different inoculations rounds of the leaf disc and detached pod tests. Such correlations were generally significant for both tests. For the leaf disc test, as expected, correlations were lower for individuals within seedling progenies than for the average of seedling progenies or of clones. This suggests that a higher number of replicate observations are required for correct evaluation of individual seedlings than for evaluation of the average level of resistance of progenies. Observations carried out 5 or 7 days after inoculation was highly correlated, suggesting that scoring in the leaf disc test may be done only once at 5, 6 or 7 days after inoculation. In one experiment the ranking of leaf disc and detached pod inoculation test results could be compared statistically, with data being significantly correlated ( r 0.78). The reliability of the tests was evaluated by the correlations between results of the tests and the level of field infection. These were generally positive and significant, for the leaf disc and detached pod test. A variation between mean scores of 5 and 8 in the detached pod test appeared to be related to a 40% difference in field infection with P. megakarya in years with medium disease pressure. However, correlations with field resistance were not always significant, suggesting the influence of uncontrolled environmental factors affecting field observations or the results in the screening tests. It is concluded that the leaf disc and detached pod tests, if applied under standardized conditions, can be of great value to speed up selection for Ppr resistance.