Site Description

The study involved storage and field experiments conducted in 2019 at the Ayepe research station of the Department of Agronomy, University of Ibadan, at Isokan Local Government Area, Osun State, Nigeria. The coordinates of the location were Latitude 7.288029°N and Longitude 4.284788°E. The vegetative descriptions at the location were reported by UN-Habitat (2014), while the prevailing relative humidity, temperature, and rainfall were obtained from NASA POWER project (Table 1).

Table 1: The weather conditions at the experimental site in 2019.

Treatments and Experimental Design

The treatments for the storage conditions involved corms stored under shade, corms stored in pits, and corms stored on raised platforms evaluated for three months (January to April) in a completely randomized design with three replicates. The treatments for the field experiments (from April to December) were the establishment of the corms collected from freshly harvested corms (S1) and the various storage conditions (corms stored under shade (S2), corms stored in pits (S3) and corms stored on raised platforms (S4) carried out in a randomized complete block design with three replications.

Storage Experiment

Cocoyam corms of 150 to 200 g that were healthy, and without wounds or any physical primary injuries were separated and bulked for the different storage methods study. The S1 corms were collected from the research field of the Department at Ayepe, while the S2 corms were stored under the shade of cassia trees. A pit of 1 m in length, 1 m breath, and 0.5 m deep was constructed and corms were placed at the bottom of the pit, then covered with palm frond for the S3 storage condition. Raised platforms for the S4 were erected from bamboo sticks, one meter high above ground level. The corms were covered with palm fronds in all the storage conditions, except for the freshly harvested corms. The freshly harvested corms were the undisturbed corms collected from under cocoa and kola nut trees as practiced by farmers and planted directly at the time of field establishment.

Field Establishment and Management

The vegetation was manually cleared, and the refuse was removed from the plot marked out for the study. Each plot size was 5 m x 5 m per plot and 1 m between plots. Heaps were manually constructed at 1 m x 1 m apart. From the stored corms, good corms (150 to 200 g each) were selected as planting materials from each of the storage methods on 26/4/2019. Planting was done by planting one corm per heap. One plant per heap was maintained to reduce overcrowding by regularly rouging out every other offshoot from the main stalk. Weeding operations were manually carried out on the field at 4, 8, and 12 weeks after planting. Subsequently, weeding of the plot was carried out, when necessary.

Data Collections

Data were collected on corm weight loss in storage after three months of storage by measuring the corm weight before and after storage for each storage condition and expressing the result in percentages (Equation 1). The storage efficiency was calculated by determining the percentages of the good corms after storage (Equation 2). The storage loss and storage efficiency were determined after three months (January - April 2019) in storage.

The rate of corm emergence was determined at 2, 4, 6 and 8 weeks after planting (WAP). Cocoyam height (the tallest petiole of the leaves that stand erect from the underground corm) was measured using a ruler. The stem diameter (the base of the leaves petiole from the underground corm) was determined using a Vernier caliper starting from the 12th WAP and continued at monthly intervals for seven months. Harvesting of the corms and cormels were done 9 months after planting as practiced by farmers in the locality. At harvest, corm and cormel length (using a ruler) and diameter (using a Vernier caliper) were measured. The weight of corms ha^-1, the number of cormels ha^-1 and cormel ha^-1 were determined using the Camry dial scale model SP-20.

Data Analysis

The observed data were subjected to descriptive statistics and analysis of variance and the significantly different means were separated using Least Significant Difference (LSD) at P<0.05.

Corms weight loss and the efficiency of different storage conditions

Weight loss in taro corm was significantly (P<0.05) affected by the storage conditions (Table 2). The corm stored under S2 had the least weight loss, while the corm stored in S4 had the highest weight loss. Weight loss during storage in cocoyam (aroids) like every other root and tuber crop has always been attributed to moisture loss, physical damage, and deterioration resulting from physiological activities and rodent attacks (Ubalua et al. 2016; More et al. 2019). This loss in weight conforms with Eze and Nwani (2014) report that tannia lose more weight in storage than taro, due to the higher moisture content in tannia than taro. A similar result was reported by USAID and CIP (2015), which stated that storage in the pit was more appropriate for sweet potatoes than the other traditional methods due to minimal deterioration through moisture loss, sprouting, and pathological losses.

Table 2: Influence of storage on corms weight loss and the efficiency of the storage conditions.

The storage efficiency varied significantly (P<0.05) for storage methods and had a similar trend with the weight loss observed (Table 2). Storing cocoyam corms under S2 gave the highest storage efficiency and retained the number of corms stored by 10.52 and 29.92% more than S3 and S4, respectively. Also, the least efficient method for storing corm is S4. The finding conforms with Behailu et al. (2023) report that using a raised platform for storing cocoyam corm resulted in propagule with the lowest quality of the storage methods evaluated. The inefficiency of the storage method is attributed to a higher rate of evaporation and transpiration that leads to increased rotting and loss of stored materials (Eze and Ameh 2011). According to Baidoo et al. (2014) and Diaguna et al. (2023) rotting of taro in storage starts after two weeks of storage. The time spent by the corms under the different conditions was long enough to facilitate an enormous level of rotting of the corms. For the corms to have stayed three months under the various storage conditions, the pathogens responsible for rotting would have ample time to cause more damage than necessary (Eze and Ameh 2011). The loss of 17.5 (corm) and 40.6% (cormel) under prolonged storage have also been reported by Diaguna et al. (2023). The observed results indicated that the use of S4 in storing propagules was most inefficient compared to the other methods, while the efficiency of S2 was the highest.

Emergence of cocoyam as influenced by corm storage methods

The emergence of the corms obtained from different storage conditions is shown in Figure 1. The corms obtained from S2 had significantly (P<0.05) higher emergence than the S4 at 2 WAP but were similar to the other treatments. While the corms from the other storage condition had less than 50% emergence at 2 WAP, the S2 treatment had over 70%. At 4 WAP, the corm emergence for S1, S2, and S3 were significantly higher than the S4 treatments. The delay in the emergence in S4 may result in the poor performance of crop raise from this storage method. A similar result was reported by Behailu et al. (2023) that storing corms on raised platforms reduced sprouting in cocoyam corms. The result is in support of Finch-Savage and Bassel (2016) report. According to their report the delay in emergence results in poor growth. They were able to report the relationship between weight loss and crop emergence. The poor emergence is attributed to higher weight loss that could have resulted from evapotranspiration and respiration. This may explain the delay in S4 emergence compared to S2. Early emergence in crops ensures that the stands that were established earlier develop roots that enable them to absorb nutrients and become independent of the food reserve in the propagule (Reed 2022). According to Lawles et al (2012) delayed emergence results in staggard plants on the field which may encourage early weed interference on the field and result in crop failure. The emergence at 6 WAP indicated no significant (P<0.05) variation among the different storage conditions. At 8 WAP, all the treatments achieved 100% emergency. This indicated that the variation in the early stand population was for a short time. At 6 and 8 WAP, the difference in stand count became similar, even though S1 and S3 took the lead.

Figure 1: Influence of corm storage methods on the emergence of cocoyam. S1 = Freshly harvested propagule, S2 = propagule stored under shade, S3 = propagule stored in pits, S4 = propagule stored on raised platforms.

Influence of corm storage methods on cocoyam height

The height of cocoyam as influenced by the method of corm storage over 7 months after planting (MAP) is presented in Figure 2. Despite the significant (P<0.05) delay in S4 emergence compared to S2 at 2 WAP and the slow rate to achieve 100% emergence, the plants from S4 were able to close in on S1 and the other treatments concerning height. The height of cocoyam increased progressively for 6 MAP but did not differ significantly among treatments throughout observation periods. However, while S3 and S4 treatments continued to increase in height at 7 MAP, the S1 and S2 heights declined. The increased height for S3 and S4 implied that the plants were still actively growing, while the plants from the other treatments were senescing. The decline in plant height after the maturation of the crop indicates' that the plant is undergoing senescence, except when the decline was as a result of environmental stress (Miryeganeh 2021). The lack of significant difference (P<0.05) in height throughout the growth period monitored implies the absence of appreciable variation in the plant's ability to acquire more available resources for development. Similarly, the continuous increase in the S3 and S4 heights suggests that the plants from these two treatments were actively growing, while others were approaching senescence. This could help the plants acquire more resources to increase yield. According to Finch-Savage and Bassel (2016), early attainment in complete emergence will likely increase growth and result in improved yield.

Figure 2: Cocoyam height as affected by corm storage methods. S1 = Freshly harvested propagule, S2 = propagule stored under shade, S3 = propagule stored in pits, S4 = propagule stored on raised platforms.

Cocoyam stem diameter as influenced by corm storage methods

The stem diameter of propagules planted from the different storage conditions did not differ significantly (P<0.05) throughout the observation period (Figure 3). Despite the differentials in the time for the plants to emerge, they did not show significant differences (P<0.05) in stem diameter during their growth periods. However, S3 consistently had the highest values after the observation made at 3 months after establishment. The plants from S1 had the lowest stem diameter values at 4 and 6 MAP, while S4 had the lowest value at 3 and 5 MAP. The decline in stem diameters for S1 and S2 was at 5 MAP, while the decline was at 6 MAP for plants established from S3 and S4. The fact that S3 and S4 attained the peak stem diameter by a month after S1 and S2 could indicate that the plants could further acquire more nutrients for development and improve crop yield (Miryeganeh 2021). As a consequence, variations in the onset of senescence may lead to differences in harvest times.

Figure 3: Cocoyam stem diameter as influenced by corm storage methods. S1 = Freshly harvested propagule, S2 = propagule stored under shade, S3 = propagule stored in pits, S4 = propagule stored on raised platforms.

Cocoyam corm yields as affected by propagule storage methods

The corms harvested from the propagule stored under the different conditions did not differ significantly (Figure 4). However, the yield of corms established from the S3 gave the highest value compared to the yields obtained from the other storage conditions. Nonetheless, the corm yield from S3 plant S3 were 15.22, 18.23 and 19.70% higher than the yields from S1, S2 and S4, respectively.

Figure 4: Corm yield as affected by corm storage methods. S1 = Freshly harvested propagule, S2 = propagule stored under shade, S3 = propagule stored in pits, S4 = propagule stored on raised platforms.

Cocoyam cormel yield as influenced by propagule storage methods

The influence of propagule storage conditions on the cormel yield of taro is presented in Figure 5. The highest and lowest cormel yields were observed in the S1 and S4, respectively. However, no significant variation (P<0.05) was observed among the different storage methods. The absence of substantial variation in the yields of cormels under the different storage methods could be attributed to the growth responses observed. Despite the differences in the emergence rate, the propagules from the various methods of storage performed similarly throughout the growth period. Indicating no substantial variation, the ability of the plants to outperform the plant from the other storage conditions. The result was reaffirmed by the non-significant difference (P<0.05) observed in the cormel yield. Nevertheless, the yield from plants propagated through S1 was higher by 858, 754 and 1,275 kg ha^-1 compared to the observed yield from plants propagated through S2, S3 and S4, respectively. Similarly, a report by Deshi et al. (2021) showed the yield of potatoes stored under different conditions differed from the observed yield after harvest. However, before the freshly harvested corm was collected for subsequent cropping, the sun would have scotched a larger percentage of the corm, thus limiting the available propagule for field establishment.

Figure 5: Cocoyam cormel yields as influenced by corm storage methods. S1 = Freshly harvested propagule, S2 = propagule stored under shade, S3 = propagule stored in pits, S4 = propagule stored on raised platforms.

Yield components of cocoyam as affected by the methods of propagule storage

The average length and diameter of corms and cormels produced using propagules from the different storage conditions did not differ significantly (Table 3). However, the propagule from S3 had the highest length and diameter of corms and cormels, while S2 had the lowest values. However, the lack of significant difference in the length and diameter of corms and cormels was not expected due to the absence of appreciable variation in the growth parameters monitored. This response was also reaffirmed by the number of cormels ha^-1, with no significant variation among treatments. Nonetheless, S1 differed from S2, S3, and S4 by 3.26, 10.94 and 23.23%, respectively. Although the result was not completely in support of Deshi et al. (2021), inappropriate storage conditions for seed tubers in potatoes could lead to a significant (P<0.05) reduction in crop growth. However, the magnitude of the difference indicated that the variation in growth could be a consequence of improved crop growth under better storage conditions.

Table 3: Yield components of cocoyam as affected by the methods of corm storage.

Correlation coefficient among the observed parameters

The Pearson correlation coefficient indicated a significant (P<0.05) positive relationship between weight loss and storage efficiency (Table 4). However, a significant (P<0.05) negative correlation coefficient was observed between weight loss in storage and corm emergence at 2 and 4 WAP. Although the weight loss also had a negative correlation coefficient with corm weight and number of cormels ha^-1, the relationship was not significant (P<0.05). The correlation coefficient indicated a significant (P<0.05) negative relationship between corm emergence at 2 WAP and the weight of cormel produced at harvest. The variation could be due to the lower rate of moisture loss in the taro compared to tannia in storage. Storage efficiency improved with a reduction in the moisture content of the stored produce (Sugri et al. 2017).

Table 4: Pearson's correlation coefficient of the parameters.