Abstract
A study has been made of the amount of variation of sugar and acid content in maturing grapes and factors affecting it. Variation in composition between vines was found to be greater than that between clusters within vines. The effect of the position of clusters on the vine and the weight of individual clusters was quite small. The mean sugar content per vine was inversely correlated with the yield of individual vines while the mean acid content was directly proportional to yield. Both the between-vine variance component and the within-vine (i.e. between cluster) variance component were highly correlated with the mean level of acid. The mean sugar content was correlated with the between-cluster variance component but not with the between-vine variance component. Irrigated grapes were more variable than non-irrigated grapes when the sugar content was less than 20 per cent. The most efficient method of sampling a plot of vines was to take a minimum amount of material per vine, i.e. one cluster if cluster sampling is used. The standard error of the mean sugar content in plots of 200 vines was ± 0.25 per cent sugar when 1 cluster was picked from each of 25 random vines or 2 clusters were picked from each of 21 random vines. Single berry sampling gave comparable estimates of the mean sugar content, and is recommended for field assessment of maturity because of the lesser amount of fruit involved. Sample estimates of the mean sugar content, using cluster Sampling, compared well with the total crop. Thirty-four such comparisons were made. Biassed estimates of the mean sugar and acid contents are obtained when equal number of clusters (or berries) are sampled from each vine, due to the correlation between yield and sugar and acid content. Methods of eliminating this bias are given.
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Claims 13
Claim · model-written summary
Composition varied more between vines than between clusters within vines.
Verbatim
e0“Variation in composition between vines was found to be greater than that between clusters within vines”
Claim · model-written summary
Cluster position and weight had only a small effect on composition.
Verbatim
e0“The effect of the position of clusters on the vine and the weight of individual clusters was quite small”
Claim · model-written summary
Mean sugar content per vine was inversely correlated with vine yield.
Verbatim
e0“The mean sugar content per vine was inversely correlated with the yield of individual vines”
Claim · model-written summary
Mean acid content was directly proportional to yield.
Verbatim
e0“the mean acid content was directly proportional to yield”
t0“Grape”
Claim · model-written summary
Both between-vine and within-vine acid variance components were highly correlated with mean acid level.
Verbatim
e0“Both the between-vine variance component and the within-vine (i.e. between cluster) variance component were highly correlated with the mean level of acid”
Claim · model-written summary
Mean sugar content correlated with between-cluster variance, but not between-vine variance.
Verbatim
e0“The mean sugar content was correlated with the between-cluster variance component but not with the between-vine variance component”
t0“Grape”
Claim · model-written summary
Irrigated grapes were more variable than non-irrigated grapes below 20 per cent sugar.
Verbatim
e0“Irrigated grapes were more variable than non-irrigated grapes when the sugar content was less than 20 per cent”
Claim · model-written summary
One cluster per vine was the most efficient plot sampling method.
Verbatim
e0“The most efficient method of sampling a plot of vines was to take a minimum amount of material per vine, i.e. one cluster if cluster sampling is used”
Claim · model-written summary
Sugar mean standard error in 200-vine plots was ± 0.25 per cent with either reported cluster sampling scheme.
Verbatim
e0“The standard error of the mean sugar content in plots of 200 vines was ± 0.25 per cent sugar when 1 cluster was picked from each of 25 random vines or 2 clusters were picked from each of 21 random vines”
Claim · model-written summary
Single-berry sampling yielded comparable mean sugar estimates.
Verbatim
e0“Single berry sampling gave comparable estimates of the mean sugar content”
t0“Grape”
Claim · model-written summary
Single-berry sampling is recommended for maturity assessment because it uses less fruit.
Verbatim
e0“is recommended for field assessment of maturity because of the lesser amount of fruit involved”
t0“Grape”
Claim · model-written summary
Cluster samples gave mean sugar estimates that compared well with the whole crop.
Verbatim
e0“Sample estimates of the mean sugar content, using cluster Sampling, compared well with the total crop”
t0“Grape”
Claim · model-written summary
Equal numbers of clusters or berries per vine produced biased sugar and acid estimates.
Verbatim
e0“Biassed estimates of the mean sugar and acid contents are obtained when equal number of clusters (or berries) are sampled from each vine”