The present study investigates the potential use of a hand-held portable SPAD chlorophyll metre for rapid assessment of specific leaf area (SLA) and specific leaf nitrogen (SLN), which are surrogate measures of transpiration efficiency (TE) in 15 cultivars of peanut (A. hypogaea). The effects of sampling (leaf position, time of sampling and leaf water status) and climatic factors (solar radiation and vapour pressure deficit, VPD) on SLA and SPAD chlorophyll metre reading (SCMR) were studied in a range of peanut genotypes grown under field and greenhouse conditions. Field and greenhouse trials were conducted during the post-rainy (November to April 1997-98) and rainy seasons (July to October 1998) in Andhra Pradesh, India. The correlation between SLA and SCMR was significant (r=-0.77, P<0.01) for the second leaf from the apex but the correlation declined for leaves sampled from lower nodal positions. The diurnal fluctuation in SLA ranged from -20 to +10%, whereas SCMR was relatively unaffected by these diurnal changes. Solar radiation and VPD during the sampling period had a significant influence on the relationship between SLA and SCMR, largely through their effects on SLA. However, standardization of SLA for these environmental factors significantly improved the relationship between SLA and SCMR from -0.50 to -0.80 (P<0.01), suggesting that, when protocols for leaf sampling and SLA measurements are followed, SCMR can be a surrogate measure of SLA. There were significant relationships between SLN and SCMR (r=0.84, P<0.01) and SLN and SLA (r=-0.81, P<0.01). These significant interrelationships amongst SLA, SLN and SCMR suggested that SCMR could be used as a reliable and rapid measure to identify genotypes with low SLA or high SLN (and hence high TE) in peanut.

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Rapid Assessment of Specific Leaf Area and Leaf Nitrogen in Peanut (Arachis hypogaea L.) using a Chlorophyll Meter

Chlorophyll stability during drought might be a promising criterion for selection for drought resistance in peanut. The study describes two field trials conducted at Khon Kaen University, Thailand which investigate genotype x drought interactions in a wide range of peanut germplasm in general and assess the relationship between chlorophyll stability and genotypic performance in particular, under drought. Two field experiments (during 2003/2004 and 2004/2005 dry seasons) were conducted in a split plot design with three water regimes [field capacity, 2/3 available water (AW) and 1/3 AW] as main, and 12 peanut genotypes as subtreatments, replicated four times. Observations on total dry matter (TDM), chlorophyll density (ChlD) (chlorophyll content per unit leaf area), chlorophyll content (chlorophyll content per plant) and SPAD chlorophyll meter readings (SCMR) were recorded at 30, 60 and 90 days after emergence. Transpiration (T) and transpiration efficiency (TE) were computed using the data on amount of water input and TDM. Drought stress significantly reduced TDM, T and chlorophyll content across genotypes but significantly increased TE and ChlD in peanut. However, there were significant differences among genotypes for TE and chlorophyll parameters. The genotype x drought interaction effects for chlorophyll characters (content and density) were not significant suggesting a strong genetic effect. The correlation coefficients between TDM and chlorophyll content (r = 0.51, P = 0.01 to r = 0.91, P = 0.01) and between TE and ChlD (r = 0.46, P = 0.05 to r = 0.77, P = 0.01) were positive and significant. These findings suggest that chlorophyll parameters are strongly linked with drought tolerance in peanut. There were highly significant and positive relationships between ChlD and SCMR (r = 0.67, P = 0.01 to r = 0.93, P = 0.01), between SCMR and TE (r = 0.41, P = 0.05 to r = 0.80, P = 0.01) suggesting that SCMR could be used as a tool for rapid assessment of relative chlorophyll status in peanut genotypes as well as for the indirect selection of drought tolerance in peanut.

Chlorophyll Stability is an Indicator of Drought Tolerance in Peanut

Two pot experiments were conducted in two different seasons at the University of Agricultural Science, Bangalore, India, to study (a) the relationship between chlorophyll concentration (by measuring the leaf light-transmittance characteristics using a SPAD metre) and transpiration efficiency (TE) and (b) the effect of leaf N on chlorophyll and TE relationship in peanut. In Experiment (Expt) I, six peanut genotypes with wide genetic variation for the specific leaf area (SLA) were used. In Expt II, three non-nodulating isogenic lines were used to study the effect of N levels on leaf chlorophyll concentration–TE relationship without potential confounding effects in biological nitrogen fixation. Leaf N was manipulated by applying N fertiliser in Expt II. Chlorophyll concentration, TE (g dry matter kg−1 of H2O transpired, measured using gravimetric method), specific leaf nitrogen (g N m−2, SLN), SLA (cm2 g−1), carbon isotope composition (Δ13C) were determined in the leaves sampled during the treatment period (35–55 days after sowing) in the two experiments. Results showed that the leaf chlorophyll concentration expressed as soil plant analytical development (SPAD) chlorophyll metre reading (SCMR) varied significantly among genotypes in Expt I and as a result of N application in Expt II. Changes in leaf N levels were strongly associated with changes in SCMR, TE and Δ13C. In both the experiments, a significant positive relationship between SCMR and TE with similar slopes but differing intercepts was noticed. However, correction of TE for seasonal differences in vapour pressure deficit (VPD) between the two experiments resulted in a single and stronger relationship between SCMR and TE. There was a significant inverse relationship between SCMR and Δ13C, suggesting a close linkage between chlorophyll concentration and Δ13C in peanut. This study provides the first evidence for a significant positive relationship between TE and leaf chlorophyll concentration in peanut. The study also describes the effect of growing environment on the relationships among SLA, SLN and SCMR.

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Leaf chlorophyll concentration relates to transpiration efficiency in peanut

Conservation of soil water resulting from
decreases in stomata conductance under atmospheric
high vapor pressure defi cit (VPD) conditions
is a possible approach for enhanced
tolerance of water defi cit by crops. Water defi cit
is usually a concern in peanut (Arachis hypogea
L.) since it is frequently grown on sandy soils
with low water-holding capacity. Seventeen peanut
genotypes were studied to determine the
response of their transpiration rates (TR) to VPD.
The results of this study demonstrated variation
among peanut genotypes with nine genotypes
exhibiting a breakpoint in their VPD response
at about 2.2 kPa, above which there was little
or no further increase in TR. Therefore, these
genotypes with a breakpoint have the possibility
of soil water conservation when VPD exceeded
2.2 kPa. The remaining eight genotypes had a linear
response in TR over the whole range of tested
VPD. Also, the 17 genotypes could be separated
into groups with differing rates of increasing TR
at low VPD. The change in TR with increasing
VPD may be important in determining the rate at
which soil water is used under fi eld conditions.

/pdf/genotypic-variation-in-peanut-for-transpiration-response-to-3wfh1d4r07.pdf

Genotypic variation in peanut for transpiration response to vapor pressure deficit

Limited-transpiration response to high vapor pressure deficit in crop species

The objective of this study was to compare the variability among advanced large-seeded 'Georgia Browne' mutant breeding lines induced by gamma-irradiation. Seeds of the small-seeded, high-yielding, disease-resistant peanut cultivar 'Georgia Browne' were exposed to a 200 Gy dose of gamma-radiation. Several advanced (M(6:7)-M(6:9)) 'Georgia Browne' mutant breeding lines were developed and evaluated at the University of Georgia, Coastal Plain Experiment Station over three consecutive years 1997-99 for disease incidence, pod yield, total sound mature kernels (TSMK) grade, pod weight, seed weight and seed size distribution. Field performance tests showed significant differences among the advanced large-seeded mutant breeding lines compared with 'Georgia Browne' for each of these variables. The results obtained demonstrate the beneficial use of mutation breeding for inducing and developing variable and desirable advanced mutant breeding lines within peanut cultivars.

Variability among advanced gamma‐irradiation induced large‐seeded mutant breeding lines in the ‘Georgia Browne’ peanut cultivar

Crosses were made between two widely grown U.S. peanut (Arachis hypogaea L.) cultivars, ‘Florunner’ and Florigiant’, and two genotypes adapted to growing conditions on the plateau of tropical Africa, ‘Makulu Red’ and 486 GKP. F2 seed populations were equally divided between Georgia and Zimbabwe. Subsequently, pedigree selection was practised simultaneously at both locations in the early segregating generations. The highest yielding pureline selections were then interchanged, and combined yield evaluations were determined over three growing seasons at each location.

‘Florunner’, ‘Florigiant’, and the Georgia pureline selections tested at the Georgia location had significantly higher pod yields than ‘Makulu Red’, 486 GKP, and the Zimbabwe selections. Conversely, the mean yield of the Zimbabwe selections tested m Zimbabwe was significantly higher than that of the Georgia selections. Thus, the breeding environment under which selection is conducted among cross populations strongly influences the yield adaptability of selected peanut genotypes

/pdf/pod-yield-comparison-of-pure-line-peanut-selections-x1oqx7vir7.pdf

Pod Yield Comparison of Pure-Line Peanut Selections Simultaneously Developed from Georgia and Zimbabwe Breeding Programs

The cultivated peanut is classified as an allotetraploid species. During the past several years, abnormal plants with coarse stems, thick leaves and an occasional single seed per pod have been found within different cultivars and advanced breeding lines. The spontaneous natural occurrence of these plants has been very rare, and frequently they do not produce any pods or seed. However, over a 3-year period (2001–2003), four individual plant selections with one mature seed per plant were found and saved. In 2003, another similar plant was also found that had the same plant characteristics, except for a single branch that had normal leaves with typical two-seeded pods. A greenhouse study was conducted during the winter of 2003–2004. The four coarse stem individual plant selections from the previous years were planted along with the check cultivar ‘Georgia Green’ and the sectorial plant found in 2003. S1 seed from both the one-seeded pods as well as normal two-seeded pods were planted from the sectorial plant. Relative DNA content was measured by flow cytometry on all plants. Results from the test showed that the coarse stem, thick leaf plants with poor fruit set were autooctoploids and had about twice the DNA content when compared with the normal sectorial branch and the allotetraploid peanut cultigen.

W. D. Branch

Papers

Variability among advanced gamma‐irradiation induced large‐seeded mutant breeding lines in the ‘Georgia Browne’ peanut cultivar

Pod Yield Comparison of Pure-Line Peanut Selections Simultaneously Developed from Georgia and Zimbabwe Breeding Programs

Natural occurrence of autopolyploidy within the allotetraploid-cultivated peanut