ENVIRONMENTAL CONDITIONS TO OBTAIN THE MOST NUTRITIOUS FODDER FROM GIANT AND COMMON LEUCAENA LEUCOCEPHALA

Date
2022
Authors
Bageel, Ahmed Mohammed
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Borthakur, Dulal
Department
Molecular Biosciences and Bioengineering
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Abstract
The foliage of both giant and common leucaena is used as a fodder for farm animals because of its high protein content and palatability. In spite of its high protein content, leucaena foliage is used only as a complementary fodder with grasses because of the presence of mimosine and tannin in the foliage in high concentrations. The presence of mimosine in the foliage is undesirable because it is toxic to animals. Similarly, high concentration of tannin is undesirable because it interferes with nutrient uptake in animals. The goal of this project was to determine the optimum growth conditions for leucaena where the foliage will contain high protein content, and lower concentrations of mimosine and tannin. The specific objectives were (i) quantifying mimosine, tannin, protein, and structural fibers in giant and common leucaena from nine different locations around the Island of Oahu; (ii) determining the effects of soil pH and salinity, age of the leaves, postharvest storage duration, and psyllid infection on the nutritional qualities of leucaena fodder; and (iii) transcriptional analysis of genes for mimosine and tannin metabolism in giant leucaena. The foliage of giant leucaena produced 14% more protein, 27% less mimosine, and 48% less total tannins than common leucaena growing in the same locations. When the nutritional qualities were compared between pruned and unpruned giant leucaena, the pruned plants contained 11% more protein, 4-5 times more mimosine, and 34% more total tannins than unpruned plants. Among five pH levels tested, pH 6.0 produced the highest amounts of protein and structural fibers in the foliage. Mimosine contents were highest at pH 6 and 7 and lowest at pH 5.0. The growth of giant leucaena was retarded and the nutritional quality were adversely affected under salinity conditions. Compared to young leaves, old leaves contained 18.5% less protein, 95% less mimosine, 30% less tannin and 40% more structural fibers. Postharvest storage duration up to 72 h, at room temperature did not affect protein, tannin and structural fiber contents of the foliage; however, mimosine content was reduced by 25%. Transcription sequence analyses of giant and common leucaena showed that the coding sequences of genes for mimosine and tannin biosynthesis were mostly identical; however, quantitative PCR analyses showed that the expression levels of genes varied greatly between the two leucaena subspecies. Mimosine concentration in the foliage appears to be directly correlated with mimosine synthase expression. The expression of mimosine synthase was significantly higher in the leucaena foliage under nitrogen abundant condition than in nitrogen deficiency condition. Mimosine concentration in the leucaena foliage was negatively correlated with salt concentrations in the soil. Mimosinase expression was three folds higher under nitrogen deficiency condition than in nitrogen abundance condition. Higher level expression of the major tannin biosynthesis genes resulted in higher tannin concentration in the foliage of giant leucaena grown under nitrogen abundance conditions. These results will help to identify ideal soil pH, age of foliage, and postharvest storage duration for obtaining high forage yield and nutritional quality for giant leucaena.
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Biology, Biochemistry, Leucaena, Mimosine, Protein, Tannin
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122 pages
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