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Genotypic Differences in Soybean Affecting the Rates of Assimilate Transport from the Leaf 1
Author(s) -
Hanson W. D.,
Kenny S. T.
Publication year - 1985
Publication title -
crop science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.76
H-Index - 147
eISSN - 1435-0653
pISSN - 0011-183X
DOI - 10.2135/cropsci1985.0011183x002500020008x
Subject(s) - petiole (insect anatomy) , biology , phloem , horticulture , sucrose , botany , sink (geography) , hybrid , agronomy , hymenoptera , biochemistry , cartography , geography
Six soybean lines [ Glycine max (L.) Merr.] differing in growth rates and 15 lines differing in cross‐sectional phloem areas in the petiole were selected for study. The objective was to identify and assess genetic differences that affect assimilate transfer. The 14 C‐assimilate transport from the fifth leaf of plants in the V7 to V8 growth stage was evaluated. The source‐sink relationship for the fifth leaf was standarized among genotypes with respect to its leaf area (source) and axillary branch initials with developing leaves (sinks). Source‐sink manipulations involved removal of either the branch initials or source leaves other than the fifth leaf (defoliation). A l‐in‐20 divergent selection among field‐grown genotypes for petiole diameter scores created a 28% difference among genotypes for cross‐sectional phloem areas in the petiole. Under the selected source‐sink balance, genotypes had similar transport velocities and specific mass transfers but had different relative mass transfer rates. The transport differences were associated with comparisons having different phloem areas. Thus, no restriction to assimilate transfer could be associated with specific genotypes other than transport capacity. The initial response to decreasing source relative to sinks was the reduction of total sucrose in the petiole. Both transport velocity and rate were about one‐third greater for defoliation than for control treatments. Genotypes can be selected which have larger phloem area but the existing vascular systems had a surprising capacity to meet increased requirements for assimilate utilization.