Genome analysis in the genus Amatanthus
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Date
1987
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Department of Olericulture, College of Horticulture, Vellanikkara
Abstract
Cytogenetical studies on eight Amananthiu species, viz.,
A. inicot-Qn./ A. JUvvduA/ A. vajujcLaa, A, ApAnoAUA, A, cLliAallA, A,hypochondmacuA,
A. cnuentuA and/4, caudaiiu and their hydrids were undertaken to
understand their genome relationship, phylogeny and evolution. The development
and arrangement of flower cluster In AmcuiardhuA were analysed
microscopically and discussed in detail. A simple provisional key was
developed for Identification of the eight species as the existing keys were
complex and confusing. The eight species were also evaluated for their
photoperiodlc requirements and antinutritional factors.
Meiotic studies revealed that members of section Blitopsis had x = 17
while section Amaranthus had x = 16 and 17. A.duLuu a polyploid with
n = 32 behaved as an allopolyploid. Mean number of chiasmata/bivalent
was maximum in the cultivated species and minimum in the semiwild
species, A ,apaiioaua which also had maximum number of rod bivalents.
Pollen grains of varying sizes (Macro and medium) were observed In all
the species. The cultivated species were characterised by bigger chromosomes
and pollen grains.
Interspecific hybridization was attempted in all possible combinations
but many of the crosses failed. A few failed crosses exhibited seedling
mortality. Seven interspecific hybrids grew and flowered and these included
hybrids within and between sections Blitopsis and Amaranthus. A .IavaduA
x. A, ioAcolon. the only interspecific hybrid within Blitopsis resembled
mostly the male parent but was highly sterile. Cytologlcal studies revealed
the presence of two or more Interchanges involving 3-6 chromosomes
and subsequent melotic abnormalities resulted in 90% pollen sterility. The
interspecific hybrids within section Amaranthus included A.^p-moAiUyA^nHinA
A , ApmoALLb x A.hypochoncbuxLCLU,, A ,4 p m o 4 iu x A , c a u d a iiu t A, A p in o itu x
A, c A u & n iiu , and A, c A ii& n tiu x A. c a u d a iiu . The hybrid A .c /u ie n iiu x
A,caudaiiu produced only female flowers in the stunted and deformed
hybrid plant. Other hybrids exhibited a preponderance of AupinoAtu characters
indicated by presence of spines, reduction in inflorescence size,
distinct placement of male and female flowers etc. Cytological studies
revealed the presence of 1-2 multivalents including 3-4 chromosomes,
moderate frequency of bivalents, and a low frequency of univalents in the
hybrids. Chromosomal repatterning through translocations and inversions
are also involved in speciation within both sections Blitopsis and Amaranthus.
A, 6p u \.0Auu x A, v ia m L u , the first success of hybridization between
the two sections resulted in a short and sturdy hybrid plant with dominating
A.qunoMu characters. Cytological studies revealed that PMCs had
high frequency of bivalents and only low frequency of univalents. The
complete absence of multivalents indicated that cryptic structural changes
and genetic drift are only involved In the cytogenetic differentiation of
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the two species. D analysis of data of chromosome associations In
interspecific hybrids at metaphase I indicate the clustering of hybrids
within and between sections under the same group. This as well as
morphological studies questions the validity of the naturalness of the two
sections in AmaAO/iiJvu,
The 40 accessions available in the germplasm were classified into
different species based on detailed cytomorphological studies. Twenty one
species were ascribed to A, four to A. d u J L u u and 15 to
A. h y p o c h o n d b u j a c iiA , The reasons for low seed recovery in the A ,b u £ .o £ o A .
accession A- were also studied.
Investigations on photoperiodic response of the different species indicated
that there is precocious flowering with increase in photoperiod in
A. h y p o c h o r u d j u x L c i u , A, riidLuu and A, A p A n o A t u , Flowering was delayed
with more light in A, cniirlatiu, and A, iju.c.o&QJi while A, cAuentu&
and A, v u u x L l a were photoinsensitive. The content of antinutrient factors
in the tender leaf and stem varied from 3.60 to 5.10% for oxalate and
0.295 to 0.695% for nitrate in the different species. In general Blitopsis
had higher content of antinutrients than section Amaranthus, the only
exception being A, A p .in .o A u A of section Amaranthus.
The primitiveness of A ,apjjioaua was evident from the present
studies. This pantropical cosmopolitan weed has played a major role in
the evolution of otherAmoAaniAuAspp. Evidences were also obtained on
the origin of vegetable amaranths from grain amaranths.
Description
PhD
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