Black pod disease profile: Monitoring its outbreak in Southwest, Nigeria

Black pod disease (BPD) has been and still remains a major threat to cocoa farmers worldwide due to its annual recurrence, fast spread and highly destructive nature. The disease has caused great anxiety in many cocoa producing communities due to the inability of indigenous cocoa farmers to determine when and where BPD outbreak will take place. Twelve (12) stations were structured from four important cocoa-producing States in the Southwestern region of Nigeria. An investigation of BPD outbreak was conducted in 2015/2016 within these regions. Infected cocoa pods and topsoil samples were collected for laboratory analysis. Pests attack, cherelle wilt and BPD outbreak were seasonal with 50% chances of occurrence in all the stations. Black pod diseases outbreak was recorded in all the States (100%) during the rainy season. The disease was at its peak in August 2015 in almost all the stations (station 1 (30.0%), station 3 (23.0%), station 11 (16.0%), station 4 (9.0%), station 5 (7.0%), and station 8 (3.0%). The height of disease severity was in September 2015 (station 1 (100.0%), station 3 (96.7%), station 5 (85.7%), station 11 (84.3%), and station 4 (70.0%), with station 8 reaching the 100% mark in October 2015. Most cocoa farmlands are now being abandoned, unless concerted efforts are made to effectively manage the disease, BPD will greatly reduce cocoa production in Nigeria and around the world.


Introduction
The disease assessment was conducted both in the rainy season and dry season to determine the 114 level of variation of black pod disease outbreak and severity brought about by seasonal changes. 115 Also, the altitude of the study areas was considered in other to determine its influence on disease 116 development and spread. Therefore, the study locations were classed accordingly and the 117 observations made were grouped based on the established criterion.

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Black Pod Disease Occurrence 119 The method adapted for black pod disease incidence determination was that of Luo [22]. Cocoa  flagellum was short and located at the posterior part of the spore. The spore stained purple to 189 violet when exposed to lactophenol in cotton blue dye and were categorically attached singly at 190 the apices of the sporangiophore (Fig 4b).  attached to it by the peduncle (Fig 5e). Mature flagellated zoospores are then released into the 203 environment when there is distress or limitation in food supply (Fig 5a).

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The dispersed spores either swim towards nearby hosts based on the chemical attraction or 205 signalling from the root rhizosphere or form thick enclosures that protect them from desiccation and other adverse environmental conditions. Spore dispersion is often aided by rain splash or 207 insect activities (Fig 5). Pod infection start from cocoa pod closest to the soil and it is further 208 disseminated by the activities of insects and other rodents within the cocoa field ( Fig 5).  (Table 3). The level of black pod disease epidemics during the wet season was 100% across all the states.

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Cherelle wilt had 100% occurrence in the dry season but it was not as intensive as black pod 228 disease. Insect and Pest invasion was 81.9% as it was undetected in some of the cocoa farms 229 assessed (Table 3). There were no observable symptoms of stem canker in all the cocoa farms 230 assessed from the far end of Ondo State to the rural communities in Ogun State. Therefore, the 231 possibility of occurrence of stem canker within these regions was 0% and as such, one less 232 problem for local cocoa farmers to contend with (Table 3).        (Table 6).

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Cocoa farmlands located in regions that are below 200m above sea level (≤200m) had a slow 294 start to black pod disease development (Table 6) (Table 7).

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The overall annual estimation of BPD intensity and outbreak within Southwest, Nigeria 100.0%, respectively (Table 10). There were no observable symptoms of BPD within in the later 380 periods of the season.

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The level of black pod disease severity was milder in the early periods of the 2015/2016 cocoa 399 production season from the statutory disease assessment result documented in Table 11. It was 400 observed that the intensity of the disease was more in Osun state with mean disease severity of  values (0%). The findings were recorded in Table 11.   was no expression of the disease during the dry season (Table 12).   The same pattern of disease severity was also observed for the month of July but in this case 608 Òwenà had the highest black pod disease incidence, with other sampled points like Wáàsimi, to farmers during these periods. This was in line with the assertion made by Ziervogel et al. [31].  The same sequence for disease prevalence was earlier given by Appiah [7]. Other preceding