In the manufacture of sauerkraut, however, about 10 to 15 % of the original fresh cabbage water content is intentionally discarded as brine (DICKSON. Tuhle 6.
Hereditas 111: 17-23 (1989)
A selection index for population improvement in white cabbage (Brassica oleracea L. var. capitata) J. DAVIK
Kvithamar Agricultural Research Station, Stj@rdal,Norway
DAVIK,J. 1989. A selection index for population improvement in white cabbage (Brus.7it.u oleraceu L. var. cupituru). - Hereditus 111: 17-23. Lund, Sweden. ISSN 0018-0661. Received November 15, 1988. Accepted March 20, 1989 A genotype’s value as a parent in a synthetic, the varietal ability, can be predicted for a specific trait. For population improvement of varietal ability. the predicted value can be handled as a quantitative character and subjected to selection. The values for several traits can be combined in an index. The optimum. the base, and the desired gains indices were assessed for use in a cabbage breeding programme. Varying the number of parents in the predictors, we found an optimum to be at about four parental genotypes in the synthetic. A further increase in number of parental genotypes gave marginal increases in predicted responses, while a reduction resulted in relatively large decreases. The indices were ranked in the following order according to the predicted overall responses: optimum, base, and desired gains, the two first being almost equal. In winter white cabbage, it is possible to complete one breeding cycle each year if the general synthesizing abilities (GSAs) for growth period and weight in December are included in the index. Weight at the end of the storage period will be improved as a correlated response.
Jahn Duvik, Kvithumur Agricultural Reseurch Station, N-7500 StjQrdul, Norway
When breeding for adaptation to marginal cold cli- extent, although this index originally was developed mate areas, a short growth period and a high yield for plant selection. One reason for the reluctant attiare obvious breeding objectives. Our programme tude of practical breeders, is the difficulty of assignaims at developing white cabbage (Brassica olera- ing relative economic values to the traits in the incea L. var capitata) cultiiars for the northern parts dex (LIN 1978). Inaccurate estimation of population of Norway. Typical climate for the target area is a parameters can bias estimates of theoretical gains short but intensive growing season with relatively for the optimum index, so an index where each trait low temperatures and abundant light which com- is weighted according to its relative economic value 1962). pensate to some extent for the lack of warmth has been proposed (WILLIAMS The desired gains index of PESEKand BAKER (HEIDE1985). Commercial cultivars from central Europe are poorly adapted to these regions, but (1969) does not require assignment of economic adapted material has been developed through mass values to the traits in the index and is in this aspect fundamentally different from the optimum index. It selection by local growers. The strategy of population improvement is con- is, however, necessary to define the desired genonected to the type of variety the breeder wants to type. The index weights of the desired gains index extract from the breeding population. Thus, the sys- are chosen so that the genotypic values of the traits tem of testing in recurrent selection depends parti- are improved in the ratio defined by the desired ally on the type of variety required, e.g., on synthe- gains. The usual approach to cabbage breeding is desizing ability for synthetics (WRIGHT 1974). Predictors of a genotype’s synthesizing ability are velopment of F,-hybrids, mainly due to the demand available and have proved very efficient in breeding of homogeneous cultivars. FI-hybrids may, howsynthetics (BLJSIWI;and GLIKGIS1976; GAILAIS ever, be too expensive to develop and multiply in 1979). These predictors can be treated as quantita- a small breeding programme. If one wishes to develop synthetics, a few-parent cultivar would be tive characters upon which selection may act. Apart from theoretical considerations, selection appropriate for the same reasons. In the present case indices have not been used much in practical plant we have evaluated the expected improvement in breeding. Animal breeders have used the optimum general synthesizing ability (GSA) of a breeding I and t i A n < i , ( 1943) to acertain population sub.jected to the previously mentioned index O ~ S M I T I(1036)
18
Hereditus I 1 I (19891
J DAVIK
selection indices when differing numbers of parent\ were used in the GSA-predictorr.
where HS, stands for the general combining ability of genotype i (estimated as the performance of the HS,-progenies) and S , , is the mean character value of its selfed progeny (GALLAIS1979). Thus, each genotype had 5 general synthesizing abilities
Materials and methods
(GSAc):
Plant material and breeding procedure A sample of 105 vernalized plants was taken from a cabbage population described elsewhere ( D A V I K l989), and each split into two parts. One of the parts was transplanted to the field and openpollinated by the domestic insects, giving 105 openpollinated halfsib (HS) progenies in total. The other part was potted, raised in an insect-proof greenhouse and bud pollinated, giving 105 first generation inbred progenies (S,). Seed set was more than sufficient to lay out an experiment with two replications. Each plot consisted of 28 individuals planted in 4 rows. but only the 10 innermost individuals were harvested to reduce the effect of interplot competition. In order to account for the variation within replication, seven sub-blocks of 30 plots each were formed. The HSand Sl-progenies from a particular genotype were^ located in the same subblock. The plots were completely randomized within the subblocks. as were the sub-blocks within the replicates. Harvesting date was evaluated subjectively, firmness of the heads being the most important criterion. Since the local consumers prefer a cabbage of 1 .O1 .S kg, the plots were harvested at this stage, provided the firmness was satisfactory. After harvest the heads were weighed (wtl), bagged in nylon sacs. and stored at 0.5 to 1.0"C. Trimming and new weighing was done during the second week of December 1987 (wt2), and the last week of March 1988 (wt3). After the last trimming, dry matter (dm) content was calculated from a chopped sample of five heads per plot, ovendried at 80°C for 24 h. The growth period score (gps) of a particular plot was calculated as the difference in days between growth period of the latest harvested plot and the growth period of the plot in question. Thus, the earliest harvested plot received the highest score. and the characters to be improved were all selected in upward direct ion. The general synthesizing ability for genotype i (GSA,). was defined by WRi(iii.1 (1974) as the mean v a l u e of all \ynthetics which have parent i as one of the m parents. GSA, for each of the 105 genotypes was calculated as
GPS -the GSA for growth period score, W 1 - the GSA for harvested yield, W 2 -the GSA for weight in December, W 3 -the GSA for weight in March (after the storage period), and DM -the GSA for the dry matter content. Each of these will depend on the size of the synthetic (m) and the HS- and S1-performance.
Selection indices An index score ( I ) was calculated for each of the genotypes using I=blxl
+ bZX7,
where trait 1 is GPS and trait 2 is one of the GSAs for the weight recordings (WlLW3). The weights of the index, (b), were calculated as b = P-'Ga, optimum index (SMITH1936); b = a, base index (WILLIAMS 1962) and b = G P i d, desired gains index (PESEKand BAKER1969).
The phenotypic (P) and genotypic (G) covariance matrices were estimated from the observational model Ylja
=p
+
R,
+ S, + T)Q)k + RSi,i + errortijk),
where Y,& is the general synthesizing ability; p its expectation; R, the effect of replication (i = 1,2); S, the effect of the subblocks (j= I , ...,7 ) ; qUlkthe effect of the progenies within subblocks (k = I , ...,15); and RS,, i s the interaction term. Uppercase letters denote random effects, while lowercase Greek letters indicate fixed effects. The relative economic values (a) and the desired genetic gains ( d ) chosen were equal in phenotypic standard deviation units: and d = l o r each o f t h e indices the predicted standardized responses to selection were estimated as
llereditas I I I ( I 989)
R=i
SELECTION INDEX FOR POPULATIONIMPROVEMENT
vb'Ga b rbase and desired gains index a'Ga
as outlined by WRICKE and WEBER(1986). In the response for the desired gains one has, however, to substitute a with d. The characters of primary interest here were the GSAs for the growth period score (GPS), and for the weight after the final trimming session (W3). It is, however, desirable to select genotypes as early as possible during the storage period in order to complete one breeding cycle each year. Selection based on W2 would facilitate this, since these recordings were taken in early December. Together with GPS, WI, W2, and W3 were included successively in the indices and the correlated response of W3 was calculated. Based on the results, two traits were included in the three indices ultimately compared. For all m-values between 2 and 7 in the GSApredictors, the overall standardized response and the single trait reponses were calculated for the three indices. Having selected k candidates for making a synthetic of size m (m< = k), (&,) synthetics are possible. A first prediction of the m-Syn (i.e., a synthetic with m parents) without specific synthesizing ability is given by
m'-~yn= ( I - -1 1 2G m
+ IS, m
(1)
where G represents the mean of the general combining effects and S the mean of the S 1 from the m selected parents (GALLAIS 1984). 10 individuals were selected on the basis of each of the three assessed indices; the optimum index, the base index, and the desired gains index, and the predicted mean and best performance of the pos-
19
sible combinations for the weight in December (wt2) and the growth period score (gps) were estimated for m = 2, ...,7. The correlated responses were calculated using the covariance between the index and the correlated character, C(I,y), and their variances, V(1) and V(y), respectively,
Restricting the correlated responses was done by including the character in the optimum index and restricting its response to zero, following the general solution of MALLARD (1972) referred to by WRICKE and WEBER(1986). 'Restriction' of the desired gains was done by setting the desired gains for the character to zero (d = 0).
Results and discussion The effect of inbreeding Inbreeding resulted in a slight increase in dry matter content, and a fall in the growth period score, harvested yield and yield after storage (Table I). A high growth period score equals a short growing period, which is a prerequisite for growing storage cabbage in the target area. Although the effect of the inbreeding is a clear reduction of the growth period score, some of the S1-progenies performed well compared to the HS-progenies. In some genotypes, no negative effect of the inbreeding was observed at all. This is shown by the spread of differences, HS-S1, in Table 1. Entries where this difference was negative are those in which the S1progenies performed better than the HS-progenies.
Tuhle I . Means, minimum, and maximum for cabbage traits observed in 105 half-sib progenies (HS) and the inbred progenies ( S , ) from the same genotypes. Results from some cultivars in common use and the breeding population from where the parental genotypes originated are also given
Entries
Growth period score Mean Min Max
Harvested yield (kg pr plot) Mean Min Max
Yield after storage (kg pr plot) Mean Min Max
Dry matter content (%) Mean Min
HS-progenies S,-prugenies HS-S I
29.49 21.00 8.50
10.73 9.83 0.90
8.93 8.13 0.80
9.22 9.64 -0.41
Bartolo F,
