LIBRO-CONGRESO-CITRUS

2011. Early production was achieved by the use of high density planting, minimal pruning managements,
fertirrigation and enhancement of cross pollination using 10 to 12 hives/ha. After 2 harvest seasons, most
phenotypical variations have been observed in lemons, obtaining 164 seedless selections, 4 thornless
selections and a compact selection interesting for ornamental production. In the case of mandarins 316
plants have been described as low seeded and 14 were completely seedless. Techniques used in this program
allow shortening in 5 years the time spent obtaining new citrus varieties. The stability of mutations detected
is being evaluated and new commercial field trials will be established with the selected materials.
S02P33
Radiosensitivity of seeds and nodal segments of citrus rootstocks irradiated in vitro with γ-rays
from 60Co Tallón C.I., Porras I., and Perez-Tornero O.
Instituto Murciano de Investigación y Desarrollo Agrario y Alimentario (IMIDA), Citricultura, Spain. olalla.perez@carm.es
The first step for a breeding program through physical mutagenesis by radiation is the evaluation of the sensitivity
in the plant material. Seeds of Citrus aurantium and Citrus macrophylla and nodal segments, where the buds
were completely removed, from micropropagated explants of C. macrophylla, were used to determine their
radiosensitivity to gamma radiation. A 60 Co source of γ-rays was used to deliver doses of 0, 10, 20, 30, 40 y 50
Gy for nodal segments, or between 0 and 250 Gy for seeds. After irradiation, the loss of germination percentage
or organogenesis efficiency was measured over two consecutive culture periods and the dose resulting in a
50% loss in germination or regeneration frequency was computed as the LD50 value. For nodal segments of C.
macrophylla, the LD50 was determined as 29.2 Gy. Seeds of sour orange were the least sensitive to radiation, its
LD50 was determined at a dose of 155.6 Gy while the LD50 in seeds of C. macrophylla was of 129 Gy.
S02P34
Studies on mutation breeding for seedless and low-seeded cultivars of citrus
Tang X.L., and Ma P.Q.
Institute of Fruit Tree Research of Guangdong Academy of Agricultural Sciences, Key Laboratory of South Subtropical Fruit Biology and
Genetic Resource Utilization, Ministry of Agriculture, China. tangxlgaas@21cn.com
Mature autumn shoots were taken from the adult seedy ‘Nianju’ (Citrus reticulata) and ‘Luogangtiancheng’ (Citrus
sinensis) trees and then the leaves of the shoots were stripped. The shoots were irradiated with gamma rays
from 60 Co at the doses of 0, 4, 6 and 8 Kr with the dose rate of 230 r/min in January of 2005. All the treated buds
were single-bud-grafted on ‘Hongningmeng’ (Citrus limonia) rootstocks after irradiation treatment. The survival
rates were 93.2%, 68.4%, 41.3% and 16.5% for the 0, 4, 6 and 8 Kr treatment of ‘Nianju’, and 98.9%,84%,73%
and 57.1% of ‘Luogangtiancheng’, respectively. The plantlets were grown in the orchard in May of 2006. Through
fruit investigation for 2 years, 4 low-seeded mutants (4-10, 6-11, 6-6, 3-11) with good characters of ‘Nianju’
were screened and their seed contents were 3.3-6.6 seeds/fruit, which were remarkably less than 17.6 seeds/
fruit of the control. In the meanwhile, 4 commercial seedless mutants (5-2-1. 7-1-5, 7-3-1, 7-3-8) with good
characters of ‘Luogangtiancheng’ were screened and their seed contents were 1.1-2.7 seeds/fruit, which were
obviously less than 13.5 seeds/fruit of the control. The pollen alive rates and the pollen germination rates of the
seedless and low-seeded mutants were obviously lower than their control respectively. One of the main causes
producing seedless and low-seeded fruits was higher rate of pollen abortion.
S02P35
Agronomic performance of twenty six clones of ‘Pera’ sweet orange in São Paulo state, Brazil
Carvalho S.A., Latado R.R., Silva L.F.C., and Müller G.W.
Instituto Agronômico (IAC), Centro de Citricultura Sylvio Moreira, Brazil. sergio@centrodecitricultura.br
‘Pera’ sweet orange, one of the most important Brazilian citrus varieties, is highly susceptible to Citrus
tristeza virus (CTV), causing reduced yield and fruit quality, even on tolerant rootstocks. The ‘Pera’ IAC
XII INTERNATIONAL CITRUS CONGRESS 2012 - 55
S02