Solanum aethiopicum L. is a delicacy in the Eastern part of Nigeria. The immature fruits of Solanum aethiopicum L. are used as cooked vegetables in stews and sometimes eaten raw. The leaves and shoots are used as cooked vegetables. Igbo people of South-Eastern Nigeria traditionally welcome visitors by offering the fruits. The leaves are eaten as leafy vegetables and are actually more nutritious than the fruit. The fruits are usually harvested while still green, before the skin becomes thick. They are picked from the same plants that provide the fruit or form special leafy cultivars. Fruits of bitter cultivars are used as medicine in many African countries [1]. Medicinal applications include the use of the roots and fruits as a carminative and sedative, and to treat coelic problems and high blood pressure, leaf juice as a sedative to treat uterine complaints, an alcoholic extract of leaves as a sedative, anti-emetic and to treat tetanus after abortion, and crushed and macerated fruits as an enema [2]. Some cultivars (Aculoatum group) are occasionally used as a rootstock for tomato and eggplant [3]. Mueller et al. [4] reported that saponins contribute largely to the foam that rises to the top of the pot when you boil garden eggs, and should be carefully skimmed off. Stemphylium disease of Solanum aethiopicum was caused by Stemphylium solani [5].

As a traditional food plant in Africa, this little known vegetable has a potential to improve nutrition, boost food security, foster rural development and support sustainable land care [6]. S. aethiopicum L is a wonderful source of potassium, manganese, copper, dietary fiber, folate, magnesium, niacin, vitamin B₁, B₂, C and K (in very small quantities) [7]. Ascorbic acid is essential for the healthy formation of the bones and teeth and a powerful antioxidant whose deficiency results in scurvy with swelling of the joints and gums, loosening of the teeth and haemorrhages of the skin and mucous membranes [8]. Calories in eggplants are very low; one cup of eggplant could give 20 calories, thereby making them ideal components of low fat diets [9]. The dietary fibers help lower blood sugar and blood cholesterol in the blood [10]. Moreover, since the fat content is less, they are excellent food for weight loss diets, as eggplants are nutrient dense food and help people feel full, thereby preventing over-eating, and Obese people love eggplant nutrition and its low sodium diet is beneficial to hypertensive patients [11].

The highly soluble minerals such as Calcium (Ca), Magnesium (Mg), Phosphorus (P), Iron (Fe) and Potassium (K), help in the maintenance of acid-base balance of the hydrogen ion concentration of the body tissues, and also help complete the absorption of vitamins, proteins, fats and carbohydrates of food [12]. Ca and Fe furnish all the cells and tissues of the body with the elements and nutritional enzymes which they need; and the higher Calcium contents of Solanum aethiopicum L., suggests that they would be more advantageous to the body in the functions associated with the minerals as Calcium is required for bone and teeth formation and in the proper functioning of the nervous system [4]. Potassium is required in muscles and nerve functions [13]. According to Olaiya and Adebisi [14], Phosphorus is important in the energy transfer of nucleic acids, its value ranging from 1.83 mg/100 g, and Iron is important in the formation hemoglobin of the blood. The vegetable Solanum aethipicum L is very low in carbohydrates, fats and proteins and therefore contribute very little to the energy values of a meal [15]. The fruits of Solanum aethipicum L. are known for possessing a diverse range of alkaloids, for example, tropane alkaloids [8] and these alkaloids can be desirable, toxic, or both, though they presumably evolved because they reduce the tendency of animals to eat the plants [6].

Some work has been done on the diseases of the crop and the proximate and phytochemical analysis of the crop. However, no work has been done on the effect of pathogen on the food value of the leaves. Hence, this work is aimed at isolation and identification of the fungi associated with the leaf blight disease in the field, determination of phytochemical and nutrient composition of the fruits and the effect of the fungi on the nutrient and phytochemical composition of the leaves.

The apparently healthy fruits, leaf and the infected leaf of Solanum aethiopicum L. used in the study were obtained from Ugwulangwu in Ohaozara L.G.A of Ebonyi State of Nigeria. The sample of the apparently healthy fruits and leaves were at their mature and greenish stage when they were collected. The symptoms of on the infected leaves were at their late stage when infected leaves were collected. Figure 1 represents a picture of apparently healthy farm of the plant showing apparently healthy leaves and fruits and infected leaves. Figure 2 represent infected leaves with the symptoms.

Figure 1: Mature plants of Solanium aethiopicum showing apparently healthy fruits and leaves and infected leaves.

Figure 2: Mature leaves of Solanium aethiopicum showing symptoms of leaf blight.

Methods of isolation

The direct method of isolation of fungal pathogens was used. The plant materials (fruits and leaves) were each cleaned to remove soils or dirt’s by passing them over running water, washed with several changes of distilled water, surface sterilized with 70% ethanol and cut into small pieces (4 mm²) with sterilized scapel. The work bench was also cleaned with 70% ethanol. The cut pieces of the fruits and leaves were placed on a freshly prepared potato-Dextrose-Agar (PDA) media and incubated at room temperature 25 ± 2°C for 48hours, after which the fungal isolates were sub-cultured into pure culture and identified based on their habit and spore characteristics using the method of Barnett and Hunter [16]. The pure isolates were preserved and sub-cultured of every fresh experiment carried out with them.

Analyses of the food and mineral nutrients, vitamin C and anti-nutrients of the apparently healthy fruits and leaves, and infected leaves of Solanum aethiopicum

The freshly harvested fruits and leaves of Solanum aethiopicum termed apparently healthy and as well as the freshly harvested infected leaves analyzed in triplicate for carbohydrate, crude fibre, moisture, protein, lipid (fat); Vitamin C; mineral nutrients : anions- Nitrate,Phosphate, Phosphorus and Nitrogen; cations-Lead (Pb), Manganese (Mn), Magnesium (Mg), Zinc (Zn), Sodium (Na),Copper (Cu), Calcium (Ca) and Cadmium (Cd); and anti-nutrients- Flavonoid, Alkaloids, Saponins and Cyanogenic glycosides using standard method of AOAC [17].

Isolation and identification of the fungus

Sclerotium rolfsii was implicated in the leaf blight of Solanum aethiopicum L. Figure 1 shows the pure culture of Sclerotium rolfsii. Table 1 shows the results of the proximate composition of the apparently healthy fruits, and leaves, and the infected leaves of Solanum aethiopicum L.

Table 1: Proximate composition of the apparently healthy fruits, leaves, and the infected leaves of Solanum aethiopicum.

Investigation of the proximate composition

Results in Table 1 showed that the apparently healthy leaves of Solanum aethiopicum L. had the highest amount of protein and carbohydrates, while the infected leaves were observed to have the least amount. The vitamin C and fibre contents were highest in the apparently healthy fruits examined but least in the infected leaves used in the study. It was also observed that the lipids and ash contents were highest in the apparently healthy fruits but least in the apparently healthy leaves. The moisture content was highest in the infected leaves studied, than apparently healthy fruits and leaves. Analysis of variance (ANOVA) conducted at 95% probability proved that there was a statistical significant difference (p<0.05) in the proximate composition of food nutrient in the infected and apparently healthy leaves and fruits and on the apparently healthy leaves and infected leaves of Solanum aethiopicum L. used in the study.

Investigation of the mineral composition

Table 2 shows that the Manganese (Mn) and Sodium (Na) contents were observed to be higher in the infected leaves, than in apparently healthy leaves and fruits. Calcium (Ca) was higher in the apparently healthy fruits and infected leaves. The Zinc (Zn), Copper (Cu) and Cadmium (Cd), however, had zero contents in all the samples examined, while the level of Lead (Pb) and Magnesium (Mg) were not determined. In Table 3, Phosphorous and phosphates concentration in infected leaves are higher than those in apparently healthy leaves, while Nitrates and Nitrogen concentrations in apparently healthy fruits and leaves are higher than those in the infected leaves. Analysis of variance (ANOVA) carried out at 95% probability showed that the metallic minerals content of the apparently healthy fruits, apparently healthy leaves and the infected leaves of S. aethiopicum L. investigated were significantly different (P<0.05).

Table 2: The minerals (cations) and non–metallic (anions) content of the apparently healthy fruits leaves and infected leaves of S. aethiopicum.

Table 3: The non metalic minerals (anions) contents of the apparently healthy fruits, apparently healthy leaves and infected leaves of Solanum aethiopicum.

Investigation of the alkaloid and flavonoid composition

In Table 4, the results show that the apparently healthy leaves of the plant used in the study had the highest level of alkaloids and flavonoids, followed by those in infected leaves, but lowest in the apparently healthy fruits. Results also show that the level of saponins was highest in the apparently infected fruits, followed by those in apparently healthy leaves, fruits, but lowest in the infected leaves. The cytogenic glycosides content was however, highest in the infected leaves studied than those in apparently healthy leaves and fruits which had equal levels of cytogenic glycosides.

Table 4: The phytochemical contents of the apparently healthy fruits, and the leaves, and the infected leaves of Solanum aethiopicum.

Analysis of variance (ANOVA) carried out at 95% probability revealed that there is no statistical significant difference (P>0.05) in the phytochemical contents of the apparently healthy leaves and the infected leaves of Solanum aethiopicum L. used in the study.

Sclerotium rolfsii was isolated from the blighted leaves of Solanum aethiopicum L., the reproductive structures and spores of the fungus in are shown in Figure 3.

Figure 3: Reproductive structures and spores of Sclerotium rolfsii Mag.x20.

Table 1, results of the proximate and vitamin C content of the apparently healthy fruits, leaves and the infected leaves of Solanum aethiopicum L. showed that the compositions of protein and carbohydrates were highest in the apparently healthy leaves, while the vitamin C, fibre, lipids and ash contents were highest in the apparently healthy fruits studied. The moisture content was however, highest in the infected leaves examined. Results also show that the infected leaves had the least amount of vitamin C, fibre, protein and carbohydrates (Table 1). Analysis of variance (ANOVA) carried out at 95% probability showed that the proximate and vitamin C content of the apparently healthy fruits, leaves, and the infected leaves of Solanum aethiopicum L used in the study were significantly different (p<0.05). According to Gropper et al. [15], the shelf life of the leaves of Solanum aethiopicum L. is very short because the leaf of Solanum aethiopicum L. is very short because the leaf has high moisture content which facilitates microbial action resulting into spoilage. In the present investigation the moisture contents of both the infected and the apparently healthy leaves were relatively higher than in apparently healthy fruits with the infected leaves having the highest amount of moisture. This shows that the high moisture content of the leaves must have facilitated the fungal activities on the leaf, leading to the degradation and dissolution of the tissue by the fungi and the resultant increase in the moisture content of the infected leaves. The utilization of the vitamin C, fibre, protein and the carbohydrates content of the infected leaf by the fungal pathogen during their degradative activities on the infected leaves must be responsible for their relative decrease in the infected leaves. When compared to the apparently healthy fruits and leaves, the high ash content 1.978% and the lipid content (6.575) of the apparently healthy fruits suggest that apparently healthy fruits of Solanum aethiopicum L. are rich in organic matter.

Since the vitamin C, fibre carbohydrates and protein contents of the infected leaves have been reduced by the fungal pathogens, it means that by continued consumption of such leaves by man be will not derived enough vitamin C from them. Szeto et al. [8], has said that vitamin C deficiency could lead to scurvy with swellings of the joints and gums, loosening of the teeth and haemorrhage of the skin and mucous membrane. The deficiency of fibre could lead to a decreased in intestinal peristalsis and other forms of nutritional disorders [18].

Tables 2 and 3 shows that the manganese, sodium, phosphates and phosphorus contents were relatively higher in the infected leaves when compared to the apparently healthy fruits and leaves. This may be attributed to the conversion of the organic matter of the leaves to inorganic ions or complexes by the fungal pathogens during their degradative activities. Calcium contents of the apparently healthy leaves are higher compared to the infected leaves. The phosphorus and phosphates concentrations in infected samples might act as the energy sources for the pathogen to multiplication in the host tissues. This corroborates the claims of Brunning [19] that the micro and macro nutrients in plants are used as food by fungi and that is why they can easily attack the plants. Marzluf [20] and Hynes [21] also stated that fungi use a diverse range of organic substrates for growth including simple compounds as nitrates, ammonia, ethanol etc.

Since the present study reveals that fungal activities in the leaves can lead to a decrease in the mineral contents of the apparently healthy leaves, it means that consumption of infected leaves can result to some mineral deficiency diseases. Rezuanul et al. [12], had reported that deficiency of calcium can cause malformation of bones in young animals and that magnesium is required in the reduction of blood pressure in hypertensive patients. The high levels of sponins, alkaloids and flavonoids in apparently healthy fruits and leaves relative to that of the infected leaves was high. The present investigation agrees with NHM [6] and Mueller et al. [4], that alkaloids and saponins occur in relatively high levels in the plants of Solanum aethiopicum L. According to NHM [6] high levels of alkaloids in Solanum aethiopicum L. can be desirable, toxic or both and that they reduce the tendency of pathogens to invade the plants. Muller et al. [4], stated that saponins exhibit potent antifungal activities. The relative high levels of saponins in apparently healthy fruits and leaves of Solanum aethiopicum L in this study agrees with Mueller et al. [4]. This is due to the fact that saponins had 4.33 ± 0.01% and 0.20 ± 0.01% in apparently healthy fruits, leaves and the infected leaves of the egg plant respectively in the present findings. The levels of cytogenic glycosides were highest in the infected leaves when compared to the apparently healthy fruits and leaves. Analysis of variance (ANOVA) carried out at 95% probability however, showed that the results have no significant difference (p>0.05).

Although the anti-nutrients observed in this study largely contribute to plants” resistance to fungal attack, Rizza et al. [22], Olmstead and Palmer [23] and Martin et al. [24] had reported that massive doses of saponins in the fruits and leaves of Solanum aethiopicum L. could lead to several degrees of health hazards ranging from leaky gut to haemolysis of red blood cells, it is recommended that controlled eating of the fruits and leaves of Solanum aethiopicum L. should be done.

From the studies carried out in this research, there is a clear evidence that Sclerotium rolfsii, affect Solanum aethiopicum L. in the field and the activities of this fungi is facilitated by high moisture content of the plant, further studies may still be carried out on the plant in relation to its fungal association on the nutrient composition and the resultant effects for more discovery.