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Wheat Information
Service
Number 71: 29-31 (1990)
Spike
abnormality in interspecific wheat hybrids
S.M.S. Tomar and M. Kochumadhavan1
Division of Genetics, Indian Agricultural Research Institute, New
Delhi 110012, India
Interspecific wheat F1 hybrids between bread wheat and
wild emmer (Triticum dicoccoides Korn.) produced spike that
partially or completely lacked spikelets on the rachis. It is
presumed that the phenomemon of suppression of spikelets (absence and
incomplete development of spikelets) in the rachis is due to the
interaction of certain genetic factors in F1 hybrid.
Lethality or semi-lethality in intervarietal, interspecific and
intergeneric wheat F1 hybrids is frequently encountered.
So far in wheat, hybrid necrosis, hybrid chlorosis and hybrid
dwarfness (grass clumps) have been reported. These physiological
disorders are the result of genic interaction and lead to premature
and gradual death of certain F1 hybrids. Such
F1 hybrids, if flower, produce spike with normal spikelets
and florets.
Ten accessions of wild emmer wheat (Triticum dicoccoides
Korn, 2n = 4x = 28, genome
AABB) were earlier crossed to two Indian bread wheat (T.
aestivum L.,
2n = 6x = 42, genome AABBDD) cultivars, C306
(Ne1ne2 ch1Ch2) and Sonalika (ne1Ne2 ch1Ch2)
with the aim of identifying necrosis and chlorosis genes present
among them (Tomar et al 1988). One particular accession of T.
dicoccoides
(SWAN 248) when crossed to C306 and Sonalika produced spikes in
F1 hybrid that partially or completely lacked spikelets
from the rachis. The absence of spikelets and incomplete development
of spikelets and florets on the rachis (developmental abnormality) in
F1 hybrids have not been reported so far.
To confirm the observations, seven bread wheat cultivars, namely,
C306, Charter (new line), HD2428, Hira, Kalyasona, Sonalika and WL711
and an accession of T. sphaerococcum L. (2n =
6x = 42, genome AABBDD) were crossed as female parents to
T. dicoccoides (SWAN 248). Three reciprocal crosses
using Kalyansona, Sonalika and WL711 as male parents were also made.
The crossed seeds were sown in pots in greenhouse as well as in the
field and were provided similar conditions for growth. The
germination of F1 seeds and seedling growth up to the 3-4
tiller stage was normal. Tillers were produced profusely but the
percentage of ineffective tillers was as high as 46%. Leaves were
narrow and medium long like that of T. dicoccoides. In
a few F1 hybrids the culm was thin with reduced peduncle
length particularly in late tillers. Some of the F1
hybrids were intermediate in height. No reciprocal difference with
respect to spike morphology was observed. Spike emergence was normal
in only those tillers where apical spikelets were present; it was
very much delayed where spikelets were totally missing or only
rachilla had developed showing that the number and position of
florets on the rachis influenced the spike emergence. Suppression of
spikelets was noticed in all the F1 hybrids
(Fig.
1) except in the
cross Charter x
T. dicoccoides
where spikes with normal spikelets and florets on the rachis
were produced. All the crosses produced abnormal spikes having basal,
intermediate and apical spikelets whereas a few tillers in the WL711
x T.
dicoccoides and Kalvansona x
T. dicoccoides
crosses produced only rachis with complete absence of spikelets.
In the F1 hybrid involving C306, two out of 60 tillers (4
plants) had produced near normal spikes indicating the variable
degree of absence (suppression) of spikelets on the rachis.
Fig.
2 shows the range
of abnormality observed among the F1 hybrids with regard
to spike. These abnormalities were first noticed in the year 1985-86
among the crosses of T. dicoccoides (SWAN 248) with C306 and
Sonalika. Crosses were repeated and the partially fertile pentaploid
F1 hybrid, Sonalika x
T. dicoccoides
was selfed. Two out of eleven F2 segregants were
observed to have spikes similar to that of the F1 hybrid.
It was difficult to establish any genetic ratio as the F2
population comprised aneuploids and size of the population was very
small.
1. IARI Regional Station,
Wellington, The Nilgiris
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