Response of diploid potato mapping population to salinity stress.

Salinity is becoming a challenge for worldwide agricultural production.Since it has amajor impact on food producton, it is essential to improve salinity tolerance in the cross that provide the largest global food source among which potato is the major one.Several studies reported the remarkable effect of salinity in the reduction of potato yield and the limited success of conveentional breeding to devlop salt tolerant potato.Therefore, a strategy was adapted to dissect this complex trait to parameters that contribute to salinity tolerance and at the end tuber yield.An experiment was conducted in hydroponics at Radix,Unifarm, over a stress period of sixteen to eighteen days to examine the response of diplid potato genotypes to salinity stress, the presence of genetic vaiability for traits related to sality tolerance,heritability of the traits and their association.Accordingly, ninety four diploid potato genotypes which are progenies from a cross between parents C and E were examined based on growth parameters, chlorophyll fluorescence.The experim,ent was laid out in a RCBD with five replictions.Three of the replications (1,2, and 5) were salt treated and the rest (replication 2 and 4) were control. A salinity level of 120mM NaCl was used and the treatment was started after thirteen days of adaption. Significant interaction effect of genotype and treatment was observed on growth parameters except root length.Growth parameters whoe=wed high reduction due to salt stress (49.2% to 74.6% relative reduction) with the highest reduction in shoot fresh weight and leaf area.The interactions between genotype and treatment, and treatment effects on the number of dead leaves were not significnat after six and thirteen days of salt stress.However, significant interaction effect was observed on the number of living leaves after thirteen days of salt stress and they showed a reduction of 32.8% due to salt stress.The interaction effect of genotype and treatment on chlorophyll content (CC) of upper leaves was significant after eight and fourteen days of salt stress; and also for the lower leaves after fourteen days of salt stress.CCof upper leaves increased after eight *5.1%) and fourteen (4.. ) days of salt stress relative to the control whereas it decreased for the lower leaf (11.1%) after fourteen days of salt stress.The interaction effect of genotype and treatment ofn the dark adapted Fv/Fm of upper leaves was significnat one and nine days aftr salt stress. One day after salt stress this parameter was increased but, it showed aslight reduction (1.4%) nine days after salt stress relative to the control.After thirteen days of salt stress, the interaction between genotype and treatment and treatment effects on Fv/Fm of upper and lower leaves were not significant.In general, the effect of salinity on Fv/Fm of leaves was not consistent over the measurements done during the stress period. In genera, growth parameters reduced significntly in reponse to salt stress with the highest reduction in shoot fresh weight and leaf ara.Root length was not affected by salt stress under hydoponics.High enetic variability was observed in growth parameters and chlorophyll content in this potato population.Moreover, the heritability of these parameters was higher the potato genotypes may be observed later than thirteen dys.Its effect on deveopment of new (oung) leaves was observed later than six days of salt stress.Chlorophyll content mays not indicate salt tolerance at early stage of salt stress.The effect of salt stress on the dark adapted Fv/Fm was inconsistent over measurement periods.Hoever, Fv/Fm of lower leaf measured later in the stress period showed mod=erate positive corrl=elation with growth parameters and CC. This may suggest measuring of this parameter with extended salt stress period to observe whether it is a mechanism for salt tolerance at later period of salt stress.