Theses and Dissertations


Ritu Dhir

Issuing Body

Mississippi State University


Harkess, L. Richard

Date of Degree


Document Type

Dissertation - Open Access



Degree Name

Doctor of Philosophy


College of Agriculture and Life Sciences


Department of Plant and Soil Sciences


The development of whitening of the youngest leaves of actively growing ivy geranium (Pelargonium peltatum L.) has been observed as the season changes from late spring to summer. This study was conducted to determine the specific environmental causes of whitening, if micronutrients deficiencies cause similar whitening, whether low night temperatures can reverse whitening, and whether salicylic acid affects growth and whitening in ivy geraniums. Two cultivars, ‘Beach’ and ‘Butterfly’, with different susceptibility to whitening were chosen for this study. Elevated air temperature, but not elevated root-zone temperature, was found to be the environmental cause of whitening in ivy geranium. Elevated air temperatures severely reduced plant growth, leaf area, fresh weight, and dry weight in both cultivars. Elevated air temperature reduced photosynthetic pigments and their ratios in ivy geranium. Carotenoids and pheophytins decreased in ‘Butterfly’ at elevated air temperature. Foliar total Fe levels indicated no inhibition of Fe-uptake at elevated temperatures. Applications of Fe-chelate at elevated temperatures helped chlorophyll synthesis in ivy geraniums. Deficiency treatments of all micronutrients, Fe, Mn, Zn, S or Mg did not result in whitening in either cultivar of ivy geraniums. Salicylic acid did not affect whitening of ivy geraniums. It did not affect growth, leaf area, fresh or dry (stem, leaf or total) weight, fresh: dry weight ratio, leaf area ratio, specific leaf area or foliar nutrient (Fe, Mn, Zn, Mg and S) content in either cultivar. Cultivars varied in their response to low night temperature. ‘Beach’ reduced its plant growth and fresh to dry weight ratio whereas ‘Butterfly’ did not. Fe-chelate application did not reduce growth, leaf area, fresh weight, dry weight or fresh:dry weight ratio of either cultivar. Although Fe-application did not reduce whitening in ivy geraniums, it helped to preserve chlorophyll, particularly chlorophyll b as indicated by Chl a:b ratio in ‘Beach’. Whitening in ivy geranium is a heat stress response initially exhibited by young, developing leaves and is caused by elevated air temperatures. Whitening is the result of impaired photosynthetic pigments synthesis and/or degradation.