الفهرس 
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Abstract
The present study was conducted during two successive seasons 2022 and 2023 on thirty female Solo papaya trees (Carica papaya L.), were selected for achieving this experiment. The trees were uniform in vigor and are two years old. The chosen trees were grown in clay soil located at the nursery of Horticulture Depart. Faculty of Agriculture – El-Minia University, Minia Governorate, since water table depth not less than two meters and surface irrigation was adopted. The chosen Solo papaya trees are planted at 1.5 X 2 meters apart. The chosen trees are subjected to regular horticulture practices that were commonly applied in papaya orchards including: fertilization, surface irrigation, hoeing and pest management.
The overall aim of this experiment is to improve understanding of the influence of inoculate ‘Solo’ papaya trees with diazotrophic bacteria (Azospirillum or/and Azotobacter) on growth parameters, mineral status, yield and its component and fruit physicochemical properties.
The most important results obtained during both experimental seasons could be summarized as follows:
1- Vegetative growth: Inoculated ‘Solo’ papaya trees with diazotrophic bacteria (Azospirillum and Azotobacter bacteria) individually or in combination at different doses present positive effects in most studied vegetative characters. Regardless the concentration used, treated Solo papaya with Azospirillum shows more effective rather than those of Azotobacter or un-inoculated trees (control). On the same concerning, inoculate the trees with the two micro-organisms in combination present superior effect rather than using each one alone in terms of improve all studied vegetative parameters, except the stem girth and leaves number per tree during the first season, whereas non-significant differences were obtained.
2- Leaf chemical composition: A promotion effect was observed on chlorophylls a & b, total chlorophylls and total carotenoids as well as mineral contents in terms of percentages of N, P, K and Mg in the leaves of Solo papaya when the trees inoculated with Azospirillum or/and Azotobacter at different doses (50 ml, 100 ml and 150 ml) over the check treatments. This increment was parallel with increasing the dose from 50ml to 150 ml. Inoculated Solo papaya trees with both examined micro-organisms in combinations produced higher and significant leaf chlorophylls, total carotenoids and mineral contents rather than using each micro-organism individually. The maximum chlorophylls and total carotenoids values as well as leaves N, P, K and Mg in leaves during the two experimental seasons, except the case of phosphorus during the first season. However, non-significant differences were observed between the two highest doses of Azospirillum or/and Azotobacter.
3- Effect on yield and its component: It is clearly shown from the obtained data that inoculated ‘Solo’ papaya trees with diazotrophic bacteria (Azospirillum or/and Azotobacter) significantly was accompanied with improving yield (kg per tree), number of fruit/tree and fruit weight relative to the un-inoculated trees (control). The promotion effect of inoculations with the two spp. of diazotrophic bacteria on the yield (kg) per tree, fruit weight, fruit number/tree was in proportional related to increasing the doses used from each micro-organism. Inoculated ‘Solo’ papaya trees with Azospirillum bacteria individually shows more effective in enhancing yield (kg/tree) and its component rather than using Azotobacter bacteria individually, during the two experimental seasons. Furthermore, the trees inoculated with Azospirillum and Azotobacter in combination at highest dose (150 ml) present the highest fruit weight, fruit number per tree and yield (kg/tree), during the two seasons respectively. In the opposite side, un-inoculated trees present the lowest fruit weight, fruit number per tree and lowest yield (kg/tree). These findings were true during the two experimental seasons.
4- Effect on physical characteristics of the fruits: Remarkable and significant promotion was observed in fruit dimensions (height and diameter), fruit pulp weight and pulp/seeds in relation to inoculate the trees with Azospirillum or/and Azotobacter rather than untreated trees. However, concerning the individual inoculate of ‘Solo’ papaya trees, the trees inoculated with Azospirillum individually present best fruit dimensions rather than those inoculated with Azotobacter individually. Furthermore inoculate Solo papaya trees with both examined micro-organisms in combination shows more effective in enhancing fruit dimensions, pulp weight and pulp to seeds ratio compared to using each one individually. The data shows that, the trees inoculated with the two examined micro-organisms in combinations at 150 ml present the beset fruit dimensions (height and diameter), fruit pulp weight and pulp/seeds in both experimental seasons. On the opposite side non-significant differences in peel weight and seeds weight (g).
5: Effect on some Chemical characteristics of fruit:
5-1: Effect on fruit TSS% and fruit sugars contents: Inoculated ‘Solo’ papaya trees with two spp. of diazotrophic bacteria (Azospirillum and Azotobacter), individually or both in combination, at different doses significantly was responsible for improving fruit TSS%, reducing & non-reducing sugars% and total sugars% rather than un-inoculation trees. These findings were true during the two experimental seasons. It is clear the obtained data that, the promotion on TSS% and sugars contents of papaya fruits was associated with increasing the doses of both examined micro-organisms (from 50 ml to 150 ml). Un-significant effect on the TSS% and Sugars contents were observed due to increasing the doses of Azospirillum or/and Azotobacter from 100 ml to 150ml. Inoculation ‘Solo’ papaya trees with Azospirillum and Azotobacter, each one at 150 ml in combination, produced the highest TSS%, reducing sugars%, non-reducing sugars% and total sugars% in fruit pulp, during the two experimental seasons. On the opposite side, the lowest total soluble solids %, reducing sugars %, non-reducing sugars % and total sugars % were obtained from un-inoculated trees in both experimental seasons.
5-2: Effect on fruit total acidity% and vitamin C contents:
During the first season, all Azospirillum and Azotobacter spp. inoculations failed to significantly improve fruit total acidity and vitamin C contents. In the opposite side, it is clear from the obtained data during the second season that, inoculate ‘Solo’ papaya trees with Azospirillum or/and Azotobacter lead to significantly decrease fruit total acidity % and increasing vitamin C in comparison with un-inoculated trees (control).
Regarding the two examined micro-organisms and the doses used, in the second season, the trees inoculated with Azospirillum present lower total acidity % and higher vitamin C contents in comparison to those inoculated with Azotobacter, during both experimental seasons. Furthermore, increasing the dose from 50 ml to 150 ml, for each examined micro-organism individually or in combination was parallel with decreasing total acidity and increasing vitamin C contents, only during the second seasons. Furthermore, during the second season, the trees received both micro-organisms in combinations present lowest total acidity and higher vitamin C contents in their fruit pulp rather than those inoculated with each micro-organism individually. Then, the trees inoculated with 150 ml Azospirillum combined with 150 ml Azotobacter present the lowest total acidity and highest vitamin C contents. Contrary, un-inoculated trees produced the highest total acidity and lowest vitamin C (mg/100g F.W) in fruit pulp. It is worth to mention that non-significant differences were obtained between the two highest doses (100 ml and 150 ml).
Conclusion:
In clay loam soil, under El-Minia Governorate conditions and similar conditions, it could be recommended to inoculate ‘Solo’ papaya trees with Azospirillum and Azotobacter (each on at 150 ml. however, 1 ml = 108 spores) in order to improve vegetative growth parameters, leaves chemical composition, trees productivity (in terms of yield “kg/tree”, fruit numbers//tree and fruit weight “g”) as well as fruit physicochemical properties.