In the current study, sesame stalk was examined with or without addition of different ratios of wheat straw for the production of oyster (Pleurotus ostreatus) mushroom. One of the phases of mushroom cultivation is called mycelial growth, or "spawn running," during which time mycelium spreads from the spawn through the cultivation substrate. A robust mycelial growth is necessary for both the quantity and quality of the fruiting body of the mushroom. Mushroom mycelium is very important in the environment because they grow on lingo-cellulosic wastes and biologically degrade and convert in to beneficial product [17]. In the current study, Treatment1 (100%) sesame stalk was the best substrate for mycelial colonization followed by Treatment 2 (the blend of 75% sesame stalk and 25% wheat straw) when compared with the control treatment (100% wheat straw). Similar mycelial colonization periods were reported on the substrates of cotton [18] and wheat straw mixed with apple pomace [19]. In contrary to the current study, a fastest mycelial extension period (15 days) was reported on waste paper substrate supplemented with corn stalk [13]. The variation in mycelial colonization period might be due to the variation in environmental factors (such as pH and temperature) and the nature of the substrate. A research on Pleurotus ostreatus and Pleurotus cystidiosus reported that the optimum growth temperature for mycelium of the two species was 28°C [20]. Moreover, Pandey et al. [21] reported that oyster species showed higher mycelium growth at 30°C and pH 6. In the current study, significant variation on primordium appearance period (days) was also observed between the treatments. Figure 1 (II) of appendix 1 indicated early primordium appearance on the plastic bag containing sesame substrate since the bags transferred to the growth room. This variation is considered to be happening due to various factors including lighting, temperature, pH and humidity of the growth room as well as the nutrients present in the substrate [22]. The amount of the spawn used during inoculation of the substrates also affects the time of mycelial colonization and primordial formation [23].
Oyster mushroom fruiting bodies are said to be matured when the caps are fully expanded but not curl the edges (Fig. 1 (IV) of appendix 1). In the current study, the mean maturation period taken since primordium initiation ranged between 6.67 days to 10.67 days. A research conducted by Fufa et al. [13] on combined agricultural wastes reported that the number of days taken for maturation since pinhead formation of 4.64 days to 12.13 days which agreed to the present study. Moreover, similar fruiting body maturation days of Pleurotus ostreatus was found [19]. In contradiction to our study, faster maturation periods of 3 days to 5 days and 3.25 days to 6.00 days since primordium formation were reported by Yohannes et al. [14] and Getachew, [3], respectively. The formation, growth and coloration of mushroom fruiting bodies are directly related to temperature variation, relative humidity and aeration of the mushroom growth room [15]. In addition, the varied duration of the maturity could be due the variation of nutrients available in the substrates used for the growth of the mushroom [25].
Measuring of stipe length and cap diameters are among the important parameters in the research related to the cultivation of oyster mushroom species. Unlike the current study, shorter stipe length and cap diameter of oyster mushroom ranged between 1.4–1.9 cm and 3.8–5.2 cm was reported by Gume [26] on different substrates known as sawdust, coffee bean husks, and corncobs. However, similar results of stipe length (2.0 cm to 3.5 cm) of oyster mushroom was reported by Keneni [27]. He also reported concurrent results of cap diameter of oyster mushroom from the treatments formulated using the substrates called faba bean straw, pea straw, coffee husk and cotton seed waste. The study reported by Tesfay et al. [13] on waste paper indicated that cap diameter of the oyster mushroom was shorter (less than 7.90 cm) as compared to the current study while stipe length of the mushroom was longer (greater than 3.01 cm). Chukwurah et al. [28] revealed that the difference in cap diameter and stipe length of oyster mushroom depends on the type and combination of substrates, structure of the substrates, compactness of the substrates, physical and chemical properties of the substrates used for the cultivation of the mushroom. Mushroom fruiting bodies with larger cap diameter, shorter and thicker stipe lengths are highly acceptable in the market [29]. In the present study, Treatment 1 (100% sesame stalk) performed better producing larger cap with higher mean diameter compared to the control while the control itself performed better in terms of stipe length producing the shortest mean stipe length. However, the stipe contains more biologically important dietary fibers as compared to the cap [13]. Therefore, the nutritional importance of the mushroom stipe/stalk should not be neglected.
The main goal of mushroom cultivation is to obtain increased yield. In the current study, the fresh yield among the flushes of each treatment showed significantly (P < 0.05) different values for most of the treatments (Table 4). Besides, the average fresh total yield showed significant (P < 0.05) variation between the treatments. This indicates that Sesame straw can replace the most expensive substrates including wheat straw for the production of oyster mushroom. This result was similar with finding of Tekesete et al. [16]. However, Elattar et al. [30] found more oyster fresh yield than the present study on rice straw, wheat straw, saw dust and water hyacinth. In the current study, higher yield was recorded when compared to the findings of Emiru et al. [12] who reported a maximum fresh yield of 796.7g per a kilogram of cotton seed hull. Tekeste et al. [16] reported too lower yield (803.23g per 1 kg of moist substrate) of oyster mushroom on sesame stalk as compared to our result. Similarly, the current study indicated much higher total fresh yield than other findings [31, 25, 14]. The higher fresh yield may be obtained due the substrate is semi-composted so that the nutrients present in substrate become easily accessible to the mycelium of the oyster mushroom. In addition, yield of mushroom can depend on the chemical nature of the substrate, temperature of the growth room, relative humidity and aeration of the growth room.
Biological efficiency is defined as the conversion capacity of different substrates into mushroom fruiting bodies. In the current study, the highest and lowest biological efficiency was recorded from Treatment 1 (100% sesame stalk) and from the control group which is 185% and 90%, respectively. This is concurrent with works of Getachew [14] who reported biological efficiency ranged from 161.3–191.7% of oyster mushroom grown on different combinations of wheat straw, waste paper and cotton seed waste. However, the results of the current study was higher in biological efficiencies as compared to the results of Dissasa [11], Tesfay et al. [13] and Mastro et al. [32]. The higher and lower results of biological efficiency may be due to the variations in the structure, composition and content cellulose, hemicellulose, lignin and other compounds of the substrate. Composted substrates indicated higher biological efficiency than non-composted substrates [11]. The current study showed that sesame stalk exclusively or in combination with wheat straw is feasible for the cultivation of oyster mushroom.
The production rate of the current study was significantly different (P < 0.05) ranging the values from 2.68 (100% wheat straw) to 7.21 (the semi-composted sesame stalk). As compared to the finding of Tekeste et al. [16] who reported a production rate of oyster mushroom on sesame stalk was 1.0, the present study produced oyster mushroom at much higher rates on semi-composted sesame stalk or its combination with wheat straw. This higher production rate may be due to sesame substrate is semi-composted so that the bonds of cellulose, hemicellulose and lignin were debilitated and the nutrients available on the substrate are easily accessible by the mycelium of the mushroom.
In experimental analysis, the correlation co-efficient is a tool used to measure the strength of a relationship between two variables. Correlation coefficients of + 1.0 indicated perfect positive correlations, whereas − 1.0 indicated perfect negative correlations. The correlation values are categorized as no correlation (0.00-0.19), low correlation (0.20–0.39), medium correlation (0.40–0.59), higher correlation (0.60–0.79), and highest correlation (0.80-1.00).
In the present study, the cap diameter and stipe length of the oyster mushroom fruiting body were found to be directly proportional to the yield or biological efficiency of the mushroom. A strong positive correlation was observed between the cap diameter and yield or biological efficiency of the oyster mushroom fruiting body, with a correlation coefficient of 0.701. Additionally, there was a significant positive correlation between stipe length and yield or biological efficiency, with a correlation coefficient of 0.624. The results were similar to those reported by Abou Fayssal et al. [33]. However, Chukwurah et al. [19] reported the highest correlation coefficient (0.921) between biological efficiency and stipe length, and the highest correlation coefficient (0.990) between cap diameter and biological efficiency of oyster mushroom grown on substrates formulated from maize straw, rice bran, sawdust, palm kernel cake, and spent grain.
By analyzing Table 6, it becomes evident that the mycelial colonization period has a strong positive correlation (0.954) with the time it takes for the mushroom to mature. This finding emphasizes that faster substrate colonization leads to faster maturation and harvesting. This result was consistent with the findings of Dubey et al. [24]. Their research found that there is a positive correlation between the mycelium colonization period and the first harvest period of oyster mushrooms.