Effects Of Plant Growth Regulators On Growth And Development Of Radish(Raphanus Sativus L.)

Radish(Raphanus sativs L.)is a root vegetable crop belonging to the Brassicaceae family;it requires cool season and short day period for optimum taproot production.The radish taproot-thickening process is the most critical period for the ultimate productivity and quality formation.Plant hormones are small organic molecules that almost have a bearing on each aspect of plant growth,which is increasing crop production to meet their growing demand.Herein,experiments were conducted to explore the effects of different plant growth regulators(PGRs)on growth and yield of radish genotypes(’Nau-yh’,’XBC’and ’BX’).Two experiments were performed at the Nanjing,China(Latitude:32°03’42"N and Longitude:118°46’40" E;Elevation above sea level:22 m = 72 ft).In the first experiment,to investigate the performances of auxin,cytokinin and melatonin on the three radish cultivars,and plant responses to different applications of exogenous plant hormones,’Nau-yh’,’XBC’ and ’BX’ radish genotypes were subjected to indole-3-acetic acid(IAA)at the concentration of 0,5,10 and 20μM,respectively.The’Nau-yh’ genotype subjected alone to 0,5,10,and 20 mg/L of 6-benzyleaminopurine(6-BA)in addition to 0,10,50 and 100 μM melatonin(MT).The cultivars were grown under nursery conditions.Significant increases in the size of taproot fresh weight,storage root yield,and number and width of the leaves were found in 10 μM IAA-treated ’Nau-yh’ and’XBC’,and 10 μM MT-treated ’Nau-yh’ genotypes.In addition,the similar effects were observed in cultivar ’Nau-yh’ treated with 10 mg/L of(6-BA).Moreover,20-μM concentration IAA had a significant effect on ’BX’ fresh weight.The maximum value in total chlorophyll(a + b)content was found in ’Nau-yh’(39%)followed by ’BX’(32%)and’XBC’(29%).The concentration of chlorophyll a and b also showed variations among radish cultivars,these results indicate that the IAA(10 μM),6-BA(10 mg/L)and MT(10μM)have potential to be used as PGRs to increase radishes productivity.The aims of the second experiment(chapter 3)were to examine the effects of GA3 and paclobutrazol(PBZ)on radish taproot formation.Four treatments were applied at the pre-cortex splitting stage of ’Nau-yh’ radish plant.Foliar spray treatments including PBZ(50 mg/L),gibberellic acid(GA3):(150 mg/L)and a mix of GA3+PBZ(150+50 mg/L)were applied.The results revealed considerable improvement in taproot growth and decreased development in aerial parts after 48 days of the growth.PBZ treatment showed enhanced growth parameters notably,root weight was 33%higher than that from GA3 treatment,28%higher than that from the control(H2O),and 23%higher than that from PBZ+GA3 treatment.PBZ also significantly promoted xylem development in the taproot of radish.In contrast,the GA3 inhibited taproot growth and enhanced shoot growth in plants.Furthermore,mass spectrometry assay confirmed the absence of gibberellins in PBZ-treated plants,whereas auxin was found in all treatments.This study provided the first evidence on the applicability of PBZ in root size expansion of radish plant.Transcription levels of six GA biosynthesis genes(Rsks-1,Rsko,RsGA20ox1,RsGA3ox1,RsRGA1,RsRGL3)and a gibberellin signaling repressor RsTIR3 were examined.The GA-biosynthetic genes,Rsks-1 and Rsko were shown down-regulated in PBZ-treated plants in all three developmental stages.The DELLAs and TIR-1 genes were most abundantly expressed upon PBZ and GA3-treatment and slightly expressed in controls.Therefore,it could be inferred that DELLA and RsTIR-1 proteins were highly expressed and might destabilize the endogenous GAs in PBZ and GA3 treatments.These results indicated the PBZ could be used as a potential effective PGR for the enhancement of radish growth,thus further increasing its production.