Some Complements to Prakken's Theory

for Pigmentation of Dry Phaseolus Vulgaris Beans

 C. M. Messiaen G. Anais C. Vincent
 Stations de Pathologie vEgetale et d'Amelioration des plants
 INRA Domaine Duclos 97170 Petit-Bourg (Guadeloupe)


 Prakken's theory for seed colorations in dry Phaseolus
 Vulgaris beans is summarised. Some modifications are pro-
 posed in order to explain anomalies which appear in crosses
 between West Indian lines:
 1. the possibility of new C alleles;
 2. the existence among Haitian beans of a type of mottling
 which is not induced by C alleles;


 Very often it is not easy to make people accept new cultivars of
 food crops with shapes, sizes or colorations different from the
 traditional ones. In the West Indies, preferences are different in
 various islands for dry Phaseolus vulgaris beans. In the
 Dominican Republic people ask for large red mottled beans. The
 same type is asked for in Haiti, but with the influence of Cuban
 culture, black medium sized beans are also accepted. InJamaica,
 people like red striped pink beans, and in the French West In-
 dies, uniform red, large beans are preferred.
 People who try to breed bean varieties for yield, adaptation to
poor soils and disease resistance are therefore concerned by the
coloration of their progenies, if they want their new cultivars to
be accepted by consumers.

The Principal Genes Involved in Dry Bean Colorations,
following Prakken's Theory
 Not taking into account minor genes for dull or shiny beans, or
for a yellow eye around the hilum, the principal genes involved in
bean coloration according to Prakken (1979) are:
 1. "P" which allows coloration (all the pp beans are white,
 whatever their other genes);
 2. C, which allows full expression of the colors (the cc beans
 have pale colors); and
 3. B (braun) G (geld), V (violett), inducing brown, yellow
 and purple pigments. The reunion of P,C,B,G, and V in-
 duces the dark coloration of black beans. These genes can
 explain the coloration of white, yellow, brown, buff, pur-
 ple or black, uniformly colored beans. Striations and mot-
 tling, and also the special status of red beans remain to be
 explained.
 Mottling may be induced by the heterozygous condition CC.
This kind of mottling cannot be preserved in pure lines. It can
also be induced by the stable Cm allele of C in pure inbred lines.
But, in the same way as Cc heterozygotes, CmCm plants produce
a minority (1 to 5 %) of dark colored beans, the progeny of which
is not different from that of mottled seeds.
 This situation is still more conspicuous in striped beans, which
possess the Cst allele of C and also produce a minority of dark
beans.
 The red coloration, which can appear only in lines homozygous
for the recessive genes b,g and v, may be induced by a dominant
gene R strongly linked with C. Such beans may be uniform red
(CR), mottled red (CRm) or red striped (CRst). Fi hybrids be-
tween CR and CRst produce red mottled beans, an unstable
situation like for Cc.


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3. the existence of a third allele, rki at the rk locus, besides
 RK and rk; and
 4. the strong linkage between bright red, uniform or striped
 pod coloration, and the Crst gene.
 Two practical applications are quoted as examples.




 Red coloration can be also induced by a recessive gene rk,
 which characterizes the "Dark Red Kidney."

 Modifications or Complements to Prakken's Theory
 Necessary to Explain the Behaviour of Some Crosses
 Between West Indian Beans.
 There are probably more alleles at the C locus
 than supposed by Prakken
 When uniform colored black or red seeded interminate varie-
 ties of Haitian or South American origin ("Nicanor 2.4" from
 Haiti or "Maluquintho" from Brazil) are crossed with striped
 beans like "Miss Kelly" (Jamaica) or "KenscoffI" (Haiti) Fi plants
 do not produce mottled seeds, but rather dark ones (black or red)
 on which the naked eye can scarcely distinguish small light spots,
 like stars on a dark sky.
 We can therefore suppose that these uniform black or red
varieties possess a "stronger" C allele than the common "C" of the
other varieties.
 Among Haitian beans, we can also find pure lines in which this
coloration is stable. For example, in "Azael 178 A," obtained
from the Haitian breeder Ariel Azael, another allele probably ex-
ists at the C locus.

Some mottlings cannot be explained by the
Cc or CmCm genotypes
 Among Haitian lines there are some ("Nicanor 6.1," "Salagnac
120," "Kenscoff G") which are red or purple mottled, with large,
dark, somewhat curved, irregular mottlings on a punctuated clear
background. A minority of the beans produced by these lines are
not darker, like for Cc or CmCm genotypes, but lighter, with on-
ly the small punctuations. When crossed with Cst striated lines,
they give Fi plants producing mottled beans. The F2 plants show
a very complicated segregation with not only the parental types,
but also pale uniform colored beans, and others which show mot-
tle and stripes together. This segregation has not been fully
elucidated. It remains that there may be a kind of mottling which
cannot be explained by the alleles of the C locus.

There are probably three alleles at the rk locus
 Some West Indian lines, such as "Miss Kelly" (Jamaica) and
"Kenscoff I" (Haiti) are striped on a pink background. This pink
background behaves as recessive in crosses with CRm or CRst
varieties with white or cream background (supposed to be Rk).
In crosses with varieties which have had a coloration of the "Dark

 PROCEEDINGS of the CARIBBEAN FOOD CROPS SOCIETY-VOL. XX