Mechanisms of self- and cross -incompatibility in sweet clover, Melilotus officinalis Lam.

117 Pages·08.792 MB·English

by  Sandal, Paul Conrad

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MECIAIIMS OF SELF- AID CROSS-IHCOMPATIBILIT? IN SWEET CLOVER,
MELILOTO'S OFFICINALIS LAM.
Paul Conrad Sandal
A D issertation Submitted to the
Graduate Faculty In P artial Fulfillm ent of
The Requirements for the Degree of
DOCTOR OF PHILOSOHfr
Major Subject* Crop Breeding
Approved*
SSF'ofr,Ma|or S^i^meSb
Iowa State College
1961
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UMI Number: DP13456
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TABLE OF CONTENDS
IimiDSDQTEOX....................................................................... ......................................... 1
Jtsn&r OF LITERATURE ....................... 3
M orphological Regions Where Incom patibility Occurs . . . . . . 4
Heteromorphic Incom patibility .................... . . . . . . . . . . . . 6
Homomorphic I ncompat i b i l i t y ....................... 9
Simple personate type s te rility . . . . . . . . . . . . . 9
M odifications of the personate type of incom patibility • . 10
Polyploidy and incom patibility . . . . . . . . . 13
Member of a lle les ............................ 14
M utations of the s te rility gene 15
Physiology of in c o m p a tib ility .............................................................. 17
Incom patibility in M elllotus o fficin alis lam. ............................ . 18
MATERIALS AH© METHODS ............................ 33
EXPERIMENTAL RESULTS .......................................... 37
Self-oom patIbility Study of a Madrid Population . . . . . . . . 27
Self-com patibility Study of Selected Sj Fam ilies ............................. 30
Data from progenies grown in 1949-50 .................................. 30
Bata from progenies grown in 1950-51 ................................................ 37
SoIf-com patibility of Sg Progenies, 1950-51 . . . . . . . . . . 48
Family 129 . . . . . . . . . . . . . . . . . .................... . . 48
Family 1 4 2 ................................ 49
Family S3 . . . . . . . . . . . . . . . . . . . . . . . . 52
Family 2 2 ....................... 52
Self-com patibility of Intra-fam ily Crosses, 1950-51 . . . . . . 57
C orrelation Between Parent-Progeny Self-com patibility . . . . . 60
C ross-com patibility Studies . . . . . . . . . . . . . . . . . . 61
Fam ily 129 ............................ 63
Family 2 2 ............................ 79
Family 62 88
MSCBSSIOI . . . ............................ 93
m m& m and conclusions ......................................................102
T ? ?<.■?$
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himmmm cxw®......................... 106
ACRMOWLEDGMEOT . ....................... I ll
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INTRODUCTION
A working knowledge of the mechanisms of self- and cross-
incom patibilities in crop plants becomes important when a breeding program
is undertaken. In many breeding plans, selfing of selected plants is
required to determine the extent of segregation. In annual and biennial
plants inbreeding is necessary to m aintain germ plasm of selected and
tested plants which may ultim ately be used in controlled crosses or
synthetic strains*
Various incom patibility systems have been found in forage plants
in the comparatively short time th at greater emphasis has been placed
on th eir improvement by breeding* The personate type of s te rility has
been established in red clover and white clover. A s e lf-fe rtility gene
also has been found in these crops so that inbred lines can be estab­
lished. Self-incom patibility also is very common in orchard grass,
bromegrass and perennial rye grass populations. These cases illu stra te
the common occurrence of self-Incom patibility in economic forage plants
th at have been studied genetically. Undoubtedly many d istin ct genetic
mechanisms are responsible for the incom patibilities found in crop
plants.
The occurrence of natural self-incom patibility In plants has been a
major factor contributing to random crossing among plants to increase
v a ria b ility and m aintain heterosygosity. Natural crossing undoubtedly
has played an important part in the evolutionary development of flowering
plants. H eterosygosity also tends to mask the expression of deleterious
reoessives and thus raaintainsplant vigor generally accepted as a
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consequence of heterosygosity*
The genetic control of the se If-incom patibility observed in
M elilotus o fficin alis has not been studied as extensively as th is
phenomenon in red ©lover and white ©lover* Research reported to date
indicates th at the personate type of incom patibility and/or a complex
associate type involving many facto rs, is the mechanism which controls
self-com patibility in sweetclover* The purpose of th is study was to
estim ate the extent of self-inoom patibility in th is crop and to secure
additional evidence concerning the mechanisms involved in its expression*
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vamm op u ism tore
Many species of flowering plants exhibit the phenomenon of self-
incom patibility, In many oases cross-pollination is ineffective w ithin
certain groups of plants. Sarly reports indicate th is phenomenon as
se lf- and c ro ss-ste rility hut more recent interpretations indicate that
se lf- and cross-incom patibility are only relative terns because in many
oases some seed is produced following self- and cross-incom patible
matings* Self-incom patibility is an important breeding mechanism in
natural populations as I t encourages cross-pollination,
A survey by Bast and Park (23) in 1917 showed th at about one hundred
cases of s e lf-s te rility were known in over th irty -fiv e fam ilies. These
workers were of the opinion th at KSlreuter should probably be credited
fo r the discovery of s e lf-s te rility in plants when he reported in 1764
th at ferbaacum phoenlceum set no seed when selfed over a two-year period,
but set seed readily upon crossing. This report was considerably earlier
than the se lf-s te rility phenomenon reported by Darwin in 1872. Bast and
Park (23) were convinced a t th is time that self- and c ro ss-ste rility in
plants was heritable and both were controlled by the same genetic mech­
anism. By 1940, Bast (21) estim ated that self-incom patibility was to be
found in more than three thousand species, distributed among twenty
fam ilies* In a study of eight hundred species, s e lf-s te rility was quite
eoimon but the distribution was not at random. I t was much more frequent
in herbaceous than In woody plants. In eighteen orders of woody plants,
two showed s e lf-s te rility whereas among tw enty-five orders of herbaceous
plants, s e lf-s te rility has been found in fourteen. One reason for th is
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unequal frequency of known s e lf-ste rility may be th at the economically
important herbaceous plants haw© been mors thoroughly studied.
The greater incidence of s e lf-s te rility in the herbaceous plants is
expected if they have been derived from the woody forms a® the geological
and anatom ical evidence indicates. S e lf-ste rility must be a relatively
recent innovation in the reproductive process in view of its biological
.and genetic complexity. S e lf-ste rility insures cross-pollination and is
an im portant factor in producing v ariab ility and perpettiatea hetero­
sygosity, both genetic and stru ctu ral, in loci adjacent to s e lf-s te rility
alleles* This heterozygosity and variation, as a resu lt of se lf-s te rility ,
has undoubtedly played an important part in the evolutionary development
of the flowering plants, Sast (21). Harland and A ttack (33) expressed
the opinion that the heterozygosity enforced by self-incom patibility was
of value in m aintaining heterosis in plant populations.
Extensive reviews on the subject of incom patibilities in flowering
plants have been reported by Stout (66), Sears (62) and Lewis (52). The
careful interpretations of these workers help a reader comprehend the
general principles of incom patibilities in plants*
M orphological legions Where Incom patibility Occurs
By cytological studies Sears (62) classified three morphological
regions of the flower where the self-incom patibility phenomenon can occur*
(l) the stigm atic surface, where pollen grains fa il to germ inate, (2) the
ovule, where incompatible ovules abort and (3) in the sty le, where pollen
tub© growth is inhibited* Sears (62) reported Erassica oleraoeae var.
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