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United States Department of Agriculture

Agricultural Research Service

Research Project: CONSERVATION, CHARACTERIZATION, AND GENETIC IMPROVEMENT OF SUBTROPICAL AND TROPICAL ORNAMENTAL GERMPLASM Title: Chlorophyll a + b content and chlorophyll fluorescence in avocado

Authors
item Reed, Stewart
item Schnell Ii, Raymond
item Moore, John
item Dunn, Christopher

Submitted to: Journal of Agricultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 14, 2011
Publication Date: April 1, 2012
Citation: Reed, S.T., Schnell Ii, R.J., Moore, J.M., Dunn, C.B. 2012. Chlorophyll a + b content and chlorophyll fluorescence in avocado. Journal of Agricultural Science. 4(4):29-36.

Interpretive Summary: Avocado trees were evaluated for differences in chlorophyll content and in efficiency of photosynthesis in leaves adapted to sun and shade conditions. Total chlorophyll content by area (Chl a+bar) ranged from 981 mg m-2 to 4339 mg m-2. Chlorophyll a/b ratio (Chl a/b) ranged from 9.8 to 5.5. Trees selected from avocado varieties Tonnage and Simmonds had similar Chl a/b with a wide range in values found among trees with Tonnage and Simmonds as parents. Shade leaves contained more Chl a, Chl b and Chl a+bwt than sun leaves. Differences in Chl a/b were insignificant or greater in shade adapted leaves; this did not follow the expected sun/shade pattern. A low chlorophyll a/b ratio indicates that chloroplasts, the leaves energy apparatus, put a greater emphasis on harvesting more light over converting light to energy for growth. Chl a+bar indicates Simmonds and Tonnage trees had similar chloroplast types in both sun and shade adapted leaves. Shade leaves had a more efficient photosynthetic system than those adapted to sun. Tonnage had the largest range of total chlorophyll content between shade and sun adapted leaves. It likely has the largest genetic variation in its ability to acclimate to changing light intensities from shade to sun as the plant grows. The range in efficiency of photosynthesis found between the avocado trees tested indicates a potential for improvements through selective breeding.

Technical Abstract: One Tonnage (T) and one Simmonds (S) avocado tree and four TxS crosses were evaluated for differences in chlorophyll content and maximal quantum yield of photosystem II in sun and shade-type leaves. Total chlorophyll content by area (Chl a+bar) ranged from 981 mg m-2 in TxS240 to 4339 mg m-2 in Simmonds. Chlorophyll a/b ratio (Chl a/b) ranged from 9.8 to 5.5 in TxS238 and TxS243, respectively. Tonnage and Simmonds had similar Chl a/b with a wide range in values found among the crosses. Shade leaves contained more Chl a, Chl b and Chl a+bwt than sun leaves. Differences in Chl a/b were insignificant or greater in shade adapted leaves for all trees except TxS238; this did not follow the expected sun/shade pattern. A low chlorophyll a/b ratio indicates more light harvesting proteins and higher stacking of thylakoids. Chl a+bar indicates Simmonds, Tonnage and to a lesser extent TxS238 had dense packing of chloroplasts in both sun and shade adapted leaves. Shade leaves had more efficient Fv/Fm values than those adapted to sun for all varieties except TxS240. Tonnage had the largest range of total chlorophyll content between shade and sun adapted leaves and likely has the largest genetic variation in its ability to acclimate to changing light intensities. The range in efficiency of photosystem 11 found between the avocado varieties tested indicates a potential for improvements through selective breeding. More research is needed to evaluate the entire USDA avocado germplasm collection for traits associated with photosynthetic efficiency and to determine their heritability.

Last Modified: 12/29/2014
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