Dear Dr. Khan,
You are absolutely right that papaya is susceptible to mosaic virus but red lady papaya variety is mosaic (PRSV) virus resistance read in different journal.For your information I am giving here some quote of research paper on Papaya biology and biotechnology. Teixeira da Silva et al published in Global Science Book.Honestly, if you have any authentic report regarding this matter please post on Agri information site that will help the redlady growers and also who coming in the new venture.
Various PRSV tolerant papaya cultivars are available in
Florida-‘Cariflora’ (Conover et al. 1986), Thailand – ‘Thapra’
(Prasartsee et al. 1995), and Taiwan-‘Red Lady’ and
‘Known You No. 1’ (Story 2002). Tolerant selections may
become infected with the virus but remain symptomless or
show mild symptom expression and produce economically
useful yields (Gonsalves 1994). The horticultural characteristics
of these tolerant selections vary from the small (0.5-
0.75 kg) sweet yellow flesh fruits of ‘Cariflora’ to the larger
(1-3 kg), light to deep yellow-fleshed fruits of ‘Thapra’
(Prasartsee et al. 1995; Gonsalves et al. 2005) and ‘Known
You No. 1’, and red fleshed fruits of ‘Red Lady’ (Gonsalves
et al. 2005). The reactions of tolerant varieties to PRSV isolates
are also known to vary and depend on the challenge
virus strain. In one study with tolerant germplasm and
PRSV isolates from Jamaica, diverse reactions dependent
on the challenge isolate and disease pressure were observed
in infectivity assays under greenhouse conditions (Turner et
al. 2004). Useful reactions of no symptoms or mild symptom
expression were obtained with tolerant cultivars from
Taiwan (‘Red Lady’), Thailand (‘Thapra’) and Florida
(‘Cariflora’). In subsequent field evaluations, diverse reactions
were observed and included no foliar or fruit symptom
expression, mild foliar and some fruit symptom expression
and severe symptom expression on both foliage and fruits.
The varieties ‘Thapra’ and ‘Red Lady’ exhibited useful levels
of tolerance and good agronomic characteristics, such
as good skin and acceptable brixes (Turner et al. 2004).
Resistance against PRSV has not been found in C. papaya.
However, much effort is being expended to introduce
resistance genes from other genera in the Caricaceae even
though the resistance appears to be variable and dependent
on the geographic origin of the virus and environmental
conditions (Gonsalves et al. 2005). In the 1960s and 1970s,
monogenic resistance against PRSV was identified in several
Vasconcella species; namely, V. cundinamarcensis (formerly
pubescens), V. stipulata, V. candicans, V. quercifolia,
and V. heibornii nm pentagona (Conover 1964; Mekako
and Nakasone 1975). Later research in the 1990s in Hawaii
involved interspecific crosses and employed in vitro embryo
rescue or ovule culture techniques in an attempt to rescue
hybrid embryos of nonviable seeds (Manshardt and
Wenslaff 1989). Regenerated F1s of C. papaya x V. cundinamarcensis
showed excellent field resistance to PRSV
while similarly grown commercial papaya were all infected
with the virus. However, the F1s were sterile and backcrosses
resulted in sesquidiploids with reduced resistance.
Similar studies in the 1990s in Australia have been conducted
with local varieties and V. cundinamarcensis and V.
quercifolia using refined protocols of hybridization and
embryo rescue (Magdalita et al. 1996, 1997, 1998; Drew et
al. 2006a). Seventy five to 100% of the hybrid progenies of
V. quercifolia and V. cundinamarcensis, respectively, were
resistant to PRSV. Backcross breeding was initiated with
hybrid progeny of V. quercifolia and in 2006, the first report
of a fertile backcross was published (Drew et al. 2006b).
BC1 and BC2 were generated in Australia and the Philippines.
Marketable fruits were obtained from BC2 trees. As
for the levels of resistance against PRSV, 13% of the BC2
plants remained symptomless under greenhouse conditions
and repeated inoculations with virus. On transfer to the field
in Australia, the asymptomatic plants, however, developed
symptoms of severe infection after 9 months. It was concluded
that more than one gene is responsible for resistance in
V. quercifolia. In later studies (Drew et al. 2007) using a
bulked segregant analysis strategy, a polymorphic randomly
amplified DNA fingerprint (RAF) marker was shown to be
linked to the PRSV-P resistant phenotype and was shown to
be present in other PRSV-P resistant Vasconcellea species.
It mapped to within 6.3 cM of the predicted PRSV-P resistance
locus. The RAF marker was converted into a co-dominant
CAPS marker, diagnostic for resistance based.
Thanks
