Abstract
ABSTRACT: The aim of this study was to evaluate the performance of progenies from Citrullus lanatus var. lanatus (cultivated watermelons) when crossed with progenies from C. lanatus var. citroides (fodder watermelon with a historic of resistance to the nematode Meloidogyne enterolobii). The parents and their F1s were evaluated for resistance to this nematode. In the initial stages of eleven treatments, watermelon seedlings plantlets were transplanted to plastic bags of six kilograms once the first leaves developed. Ten inoculated plants with 5,200 eggs in the soil near the stem of the plant and four non-inoculated ones were used in each treatment, in a complete block design. Sixty-two days after sowing, the following characteristics were evaluated: the length of the aerial part of the plant (LAP, in m), fresh mass of the aerial part (FMAP, in g), root fresh mass (RFM, in g), egg number (EN) and reproduction factor (RF). A comparison between the averages of inoculated and non-inoculated plants was performed using Scott-Knott test at 5% and the diallelic analysis was performed using the GENES program. The morphological characteristics did not allow for the identification of the parent plants or the F1s with respect to nematode resistance, but the variables EN and RF were useful for such identification. The analyses of the general and specific combining abilities indicate highly significant effects with respect to this resistance, showing additive gene effects as well as dominance and epistatic gene effects, allowing for identification of parents and F1s that can be used in watermelon breeding programs to improve resistance to the M. enterolobii.
Highlights
In 2012, Brazil was ranked fourth in global production of watermelon, Citrullus lanatus (Thunb.) Matsum and Nakai var. lanatus, with a total of 2,079,547 tons produced (FAOSTAT, 2014)
Length of the aerial part (LAP) and fresh mass of the aerial part (FMAP), as measured in all parent plants and F1 progeny, showed no significant difference between inoculated plants and plants that were not inoculated
There was an increase in fresh root mass in inoculated plants for parent plants P4 and P5, and for the F1 combinations (P4 x P2), (P4 x P3), and (P5 x P3); in these genotypes, an increase in the root fresh mass (RFM) could be observed due to formation of giant cells, caused by the penetration and reproduction of nematodes on the roots of infected plants (COYNE et al, 2007; LOPES et al, 2008)
Summary
In 2012, Brazil was ranked fourth in global production of watermelon, Citrullus lanatus (Thunb.) Matsum and Nakai var. lanatus, with a total of 2,079,547 tons produced (FAOSTAT, 2014). Lanatus, with a total of 2,079,547 tons produced (FAOSTAT, 2014). Despite this high production, infections from fungi, bacteria, viruses, and nematodes cause plant diseases and biotic stress that reduce both productivity and fruit quality (SANTOS et al, 2005; SILVEIRA et al, 2005). Among these pathogens, plant-parasitic nematodes (phytonematodes that infest the root system of the watermelon plants) of the genus Meloidogyne cause irreparable losses in watermelon fields, and it may create environmental damage if nematocides are applied. Though there are no published studies addressing parasitism of M. enterolobii in watermelon, samples of infected roots sent by producers to the Nematology Laboratory at the Semi -Arid Research Center of the Brazilian Agricultural Research Corporation (Embrapa) (CASTRO, 2014, personal communication) indicate that this nematode is parasitizing watermelon roots
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