Research Article

Mutagenic Effects of Ultraviolet Radiation on Growth and Agronomic Characters in Maize Cultivars  

Olawuyi  Olawuyi O.J.1 , Bello O.B.2 , Abioye A.O.1
1 Department of Botany, University of Ibadan, Ibadan, Nigeria
2 Department of Biological Sciences, Fountain University, Osogbo, Nigeria
Author    Correspondence author
Molecular Plant Breeding, 2016, Vol. 7, No. 1   doi: 10.5376/mpb.2016.07.0001
Received: 15 Sep., 2015    Accepted: 26 Oct., 2015    Published: 01 Jan., 2016
© 2016 BioPublisher Publishing Platform
This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Preferred citation for this article:

Olawuyi O.J., Bello O.B., and Abioye A.O., 2016, Mutagenic effects of ultraviolet radiation on growth and agronomic characters in maize cultivars, Molecular Plant Breeding, 7(01): 1-10 (doi: 10.5376/mpb.2016.07.0001)

Abstract

Ultraviolet light has strong genotoxic effect to induce mutations for developing high genetic variability in yields, early maturity and other characters in crops. The study investigated the mutagenic effects of ultraviolet (UV) radiation on growth, yield, agronomic and mutation tolerance of six maize cultivars. Maize seeds were exposed to UV radiation, and planted in 7 kg soils in the polythene bags, while unexposed served as control. The effect of UV radiation on the first order interaction between weeks after planting (WAP) and treatments was only significant (p<0.05) on plant height. The interaction between treatments and cultivars also produced significant effect on all growth characters except leaf width. There was reduction in growth characters at 8 and 10 WAP for number of leaves, and at 10 WAP for plant height, leaf length and leaf width. All the growth and agronomic characters at 100 minutes of UV radiation were significantly higher (p<0.05) than other exposure periods. The exposure period of stover weight at 100 minutes were significantly higher (p<0.05) than other periods, while grain weight and total number of grains at 20 minutes exposure significantly higher, but not different from control. The height of ART/OB/98/SW1 was significantly higher than other cultivars. ART/OB/98/SW6, 10–1–Y and ART/OB/98/SW1 were the most tolerant cultivars to the mutagenic effect of the UV radiation. OBA 98 had the most significant genotypic effect for yield characters, while the genotypic influence on plant stand, plant aspect, mutation tolerance and plant harvest was highly significant. The grain weight per stand for OBA 98 and ART/OB/98/SW1 were significantly (p<0.05) higher than other cultivars, while the total number of grains for ART/0B/98/SW1 and ART/OB/98/SW6 were significantly higher and different from other cultivars. ART/OB/98/SW6 had the least values of days to plant emergence, mutation tolerance and other agronomic characters compared to other cultivars. The plant height was positive and strongly correlated (p<0.01) with leaf length, leaf width and number of leaves with r = 0.95, 0.96, 0.89 respectively. Only the periods of exposure of the UV radiation was positive and strongly correlated with leaf width (r = 0.79). The association between the stover weight and periods of exposure was positive and insignificant, while the correlation between total numbers of grains and grain weight per stand was positive and strong (r = 0.99). Therefore, quality protein maize cultivars should be improved by introgression of favourable genes of drought tolerance, grain yield and related characters through induced mutation of UV radiation.

Keywords
Maize tolerance; Mutation; Ultraviolet radiation; Yield

Introduction
Maize (Zea mays L.) is a tall, monoecious and annual nutritious plant of the family Poaceae, which shares a classification with other important agricultural crops including wheat, rice, oats, sorghum, barley and sugarcane (Ellneskog–Staam et al., 2007; Bello and Olaoye, 2009; Olawuyi et al., 2010; Fapohunda et al., 2013; Bello et al., 2014abc). There are five species in the genus of Zea with chromosome number of 2n=20, except Zea perennis (Perennial teosinte with 2n=40) (Riera–lizarazu et al., 1996; CIMMYT, 2003; Singletary, et al., 2003; Rabinowicz and Bennetzen, 2006). Maize is characterized by a wider genetic base, and adapt to wide range of changes in the environment. Maize possesses diverse morphological and physiological characters resulting from a wide genetic base available for selection (Paliwal, 2000; White, et al., 2000; Srinivasan, et al., 2004; Mano, et al., 2005; Bello, et al., 2011; 2012; Olawuyi, et al., 2015).
 
Mutation is a heritable sudden change in gene structure which opposes the wild characteristics. The abnormal changes in genetic materials alter the DNA sequence of purine and pyrimidine base pairs. Mutation could result in death of cells ranges in size from a single DNA building block to a large segment of a chromosome (Beadle and Tatum, 1959; Mertz, et al., 1964; Misra, et al., 1972; Mochida, et al., 2004; Messing and Dooner, 2006). Mutation plant breeding methods had been used in many fields as Biotechnology, Cytogenetics and Molecular Biology (Javed, et al., 2016). Mutation breeding in maize encompasses a number of approaches, including spontaneous mutation, tissue–culture induced mutation (somaclonal variation), chemical mutagenesis, transposon mutagenesis and irradiation mutagenesis (Anderson and Georgeson, 1989; Newhouse et al., 1991; Tan, et al., 2005). Induced mutation including gamma–rays, physical and chemical mutagens are prime methods for developing high genetic variability in yields, early maturity and other characters in crops, such as cereals and fruits (Acharya, et al., 2007; Javed, et al., 2016). The mutagenic effect can lead to chromosomal instability, breakages and rearrangement such as substitution, deletion and insertion of the bases, which occur through the modification of DNA sequence, and could enhance production of yield and other related characters for selective breeding in crops (Boyer and Hannah, 1994; Ahloowalia, et al., 2004; Shah, et al., 2008).
 
Ultraviolet (UV) light is a physical mutagen and electromagnetic radiation that causes adverse effect to genetic make–up of organisms, of which plants are included. It has a shorter wavelength than visible light, but longer than X–ray. UV lights had been classified into three bands based on their wavelengths as absorption maximum for nucleic acid and protein viz; i. UV light A (320 nm to 400 nm), ii. UV light B (290 nm to 320 nm) and iii. UV light C (200 nm to 280 nm). UV light A is subdivided into UV A1 (340nm to 400 nm) and UV A2 (320 nm to 340 nm) (Caldwell, et al., 2011; Tanigawa, et al., 2011).
 
UV light has strong genotoxic effect to induce mutations of which Sun ray is the major natural source. UV rays induced mutation by causing inactivation of plant genome as UV–signature and triplet mutations. The diversity of soil environments and climatic conditions as well as biotic stresses had created the basis for the development of mutant varieties of maize. Based on the foregoing assessment of gene expression of individual response genes to UV radiation in maize is very imperative. This study therefore investigated the mutagenic response of maize to exposure periods of UV radiation on growth, yield, mutation tolerance and agronomic characters.
 
1 Data Analysis
The data were statistically analyzed using the SAS software program version 9.2 (SAS Institute, 2009, Version 5). Analysis of variance (ANOVA) was computed, while the means were separated by Duncan’s Multiple Range Test (DMRT). The relationship among the growth characters, stages of growth, agronomic characters, mutagenic tolerance, exposure periods and yield of maize cultivars were also determined using Pearson correlation coefficient.
 
2 Results
Table 1 shows that the mean square effect of UV radiation on growth stages, exposure periods and cultivars produced highly significant (p<0.01) effects on the growth characters. The first order interaction of replicates and treatments had significant effect on growth characters except leaf length. Again, the effect of UV radiation on first order interaction between weeks after planting (WAP) and treatments was only significant (p<0.05) on plant height, but not significant on other growth characters. The interaction between treatments and cultivars also produced significant effects on all the growth characters except leaf width. The effect of UV radiation on WAP and cultivars was significant (p<0.01 and p<0.05) on plant height, leaf length, leaf width and number of leaves (Table 1).

 

 

Table 1 Mean square effect of ultraviolet radiation (UV) on growth characters of maize

Note: ** p< 0.01 highly significant, * p<0.05 significant, ns= non significant

  

Table 2 shows that the exposure periods of UV radiation was significantly (p<0.01) higher on plant husk, but significantly (p<0.05) affected ear aspect, ear harvest and plant harvest, while days to plant emergence, plant stand, plant aspect and mutation tolerance did not differ. The genotypic influence on plant stand, plant aspect, mutation tolerance and plant harvest however, was highly significant (Table 2). Table 3 shows that the cultivars produced significant effect on stover weight, but not differed significantly for grain weight per stand and total number of grains. The effect of the treated maize cultivars at varied exposure periods was unaffected by differences in yield characters. Table 4 shows that there are variations in performance of growth characters in maize under varied exposure periods of UV radiation. All the growth and agronomic characters at 100 minutes were significantly higher (p<0.05) than other exposure periods. On the other hand, the periods at 20, 40 and 60 minutes as well as control did not differ significantly for plant height and leaf length. Also, the mean number of leaves at 60 and 80 minutes were not significantly different.

 

 

Table 2 Mean square effect of UV radiation on agronomic characters of maize

Note: **p<0.01 highly significant, * p< 0.05 significant, ns= non–significant

  

 

Table 3 Mean square effect of UV radiation on yield characters of maize

Note: **p<0.01 highly significant, * p< 0.05 significant, ns= non–significant

  

 

Table 4 Growth performance of maize under varied exposure periods of UV radiation

Note: Means with the same letter in the same column are not significantly different at p> 0.05 using Duncan’s multiple range test

  

Table 5 shows that there were significant effect (p<0.05) of different exposure periods of UV radiation on days to plant emergence, ear aspect, plant husk, ear harvest and plant harvest, while plant stand, plant aspect and mutation tolerance produced similar effect. The period of exposure at 100 minutes was higher and highly tolerant than other exposures for days to plant emergence, mutation tolerance and other agronomic characters. The ear aspect at 40 and 80 minutes as well as control and 60 minutes were not significantly different. Table 6 shows that the exposure period of stover weight at 100 minutes is significantly higher (p<0.05) than other periods, while grain weight and total number of grains at 20 minutes are significantly higher, but not different from the control. The periods of exposure at 40 and 60 minutes as well as 80 and 100 minutes did not differ from each other for grain weight and total number of grains. Table 7 shows that all the growth characters in Cultivar ART/OB/98/SW1 are significantly higher than other cultivars. The leaf length, leaf width and number of leaves of ART/OB/98SW1 were not significantly different from 10–5–W. The number of leaves for 3–1–4 was not significantly different from 10–5–W and ART–OB–98–SW1. OBA 98 had significant reduction in mean values for all the growth characters, but not different from the plant height of 10–1–Y. The height status for OBA 98 and 10–1–Y, as well as the leaf length and leaf width for 10–1–Y and ART/OB/98/SW6 were not significantly different from one another. On the other hand, ART/OB/98/SW6 was outstanding for days to emergence and other agronomic characters compared to other cultivars, while 10–5–W was the worst. ART/OB/98/SW6, 10–1–Y and ART/OB/98/SW1 were the most tolerant cultivars to mutagenic effect of UV radiation, while 3–1–4 was most susceptible. There was an excellent contribution of genotypic effect on ear aspect, plant husk, ear harvest and plant harvest for all the cultivars though better than OBA 98 (Table 8).

 

 

Table 5 Different exposure periods of UV radiation on mutation tolerance and agronomic character of maize

Note: Means with the same letter in the same column are not significantly different at p< 0.05 using Duncan’s multiple range test, Mutational tolerance: Highly tolerant 1–3, moderately tolerant 4–6, moderately susceptible 7–8, highly susceptible 9. Drought tolerant rating: 1 is excellent, 2 is good, 3 is fairly good, 4 is fair, 5 is poor

  

 

Table 6 Effect of different exposure periods of UV radiation on the yield characters of maize

Note: Means with the same letters in the same column are not significantly different at p>0.05 using Duncan’s multiple range test

  

 

Table 7 Genotypic effect on growth characters of maize

Note: Means with the same letter in the same column are not significantly different at p>0.05 using Duncan’s multiple range tests (DMRT)

  

 

Table 8 Genotypic effect on agronomic characters and mutation tolerance of maize

Note: Means with different letters in the same column are not significantly different at p<0.05

  

Table 9 shows significant differences (p<0.05) in genotypic effect on the yield characters of maize. The mean values of stover weight for ART/OB/98/SW1 and ART/OB/98/SW6 were not significantly different from each other. The grain weight per stand for OBA 98 and ART/OB/98/SW1 were not significantly different, but higher and different from other maize cultivars. The cultivars 10–5–W and 10–1–Y for grain weight per stand were not different from each other, but higher and significantly different from cultivar 3–1–4. The total number of grains for ART/0B/98/SW1 and ART/OB/98/SW6 were significantly (p<0.05) higher, but different from other cultivars. The plant height was positive and strongly correlated (p<0.01) with leaf length, leaf width and number of leaves with r = 0.95, 0.96, 0.89 respectively. The associations among plant height, treatments and cultivars were positively insignificant (Table 10). The leaf width was positive and strongly related with plant height and leaf length with r = 0.95 and 0.94 respectively. There were strong positive associations between number of leaves and plant height, leaf length and leaf width with r = 0.89, 0.89 and 0.95 respectively. Only the periods of exposure was positive and strongly correlated with leaf width (r = 0.79) (Table 10). Table 11 shows that there was positive and strong associations between plant stand with plant aspect and mutation tolerance at r = 0.96 and 0.97 respectively, while negative and strong relationship existed between plant stand and replicates with r = –0.75. Also, plant stand was positive and strongly related with periods of exposure and plant aspect at r = 0.76 and 0.96 respectively.

 

 

Table 9 Effect of cultivars on the yield characters of maize

Note: Means with the same letter in the same column are not significantly different at p<0.05 using Duncan’s multiple range test.

  

 

Table 10 Correlation matrix of growth characters of maize

Note: **p<0.01, * p<0.05, Treatment = Periods of exposure

   

 

Table 11 Correlation matrix of the agronomic characters of maize

Note: ** Highly significant at p<0.01, * Significant at p<0.05

 

There were significant and positive correlations between ear harvest and ear aspect (r = 0.59), plant husk (r = 0.61), as well between plant husk and ear aspect (r = 0.82), while the associations between plant harvest and ear aspect (r = 0.57), plant husk (r = 0.64) and ear harvest (r = 0.90) were strong and positive (Table 11). The association between the stover weight and periods of exposure is positive and insignificant, while the correlation between total number of grains and grain weight per stand was positive and strong (r = 0.99). The association between the periods of exposure and grain weight per stand, total number of grain was negative and significant with r = –0.46 and –0.48, respectively. The cultivars are positive and strongly related with the periods of exposure at r = 0.70 (Table 11). The correlation between total number of grains and grain weight per stand however was positive and significant with r = 0.99 (Table 12).

 

 

Table 12 Correlation matrix of yield characters of six cultivars of maize

 

3 Discussion
The reduction in the growth characters at 8 and 10 WAP for number of leaves and 10 WAP for plant height, leaf length and leaf width could be due to mutagenic effect of UV radiation on maize, as similarly reported by Teramura (1983). There were variations in the contribution of the genotypic effect on growth performance of maize. ART/OB/98/SW1 showed greater tolerance to the mutagenic effect of the UV radiation, while OBA 98 could not tolerate the varied exposure periods. This could be due to the differences in the genetic make–up of the maize cultivars. The performance of ART/OB/98/SW1 and ART/0B/98/SW6 could also be attributed to the high quality protein contents in maize (Olakojo, 2004; Olaoye, et al., 2009; Bello, et al., 2014a). The least mean values of days to plant emergence for ART/OB/98/SW1 compared to 10–5–W and other cultivars showed that they have early maturity traits as similarly reported by Olawuyi, et al. (2010; 2013). This could be due to presence of early and maturing genes present in the quality protein maize. ART/OB/98/SW6, 10–1–Y and ART/OB/98 SW1 had higher tolerance to mutagenic effect of UV radiation. This could be due to the presence of tolerant genes present in the maize cultivars. Olakojo and Kogbe, (2003), Olawuyi, et al. (2011) and Bello, et al. (2014b) had earlier reported tolerance of quality protein maize cultivars to Stiga lutea and resistance to drought. Maize grain weight and total number of grains at 20 minutes and control showed the best tolerance to UV radiation compared to other periods. Though, the performance of stover weight at 100 minutes as well as at 80 and 100 minutes for grain weight and total number of grains could be due to the contribution of the  mutation tolerant gene present in some of the cultivars, particularly the quality protein maize. OBA 98 and ART/OB/98/SW1 performed appreciably in all the yield characters compared to other cultivars. The superior performance of these cultivars revealed their tolerant potential to the mutagenic effect of the UV radiation.
 
4 Conclusion and Recommendations
The quality protein maize cultivars not only showed greater tolerance to mutagenic effect of the UV radiation, but were outstanding in grain yield compared to other cultivars. It appears that the effect on exposure to UV radiation did not have deleterious effect on the growth and agronomic characters of maize, but cause reduction in grain yield on exposure to UV radiation at longer periods. Therefore, quality protein maize cultivars should be improved by introgression of favourable genes of drought tolerance, grain yield and related characters through induced mutation of UV radiation. The characters evaluated from correlation analysis should further be encouraged and explored in the breeding programmes.
 
5 Materials and Methods
5.1 Germplasm
Six maize cultivars were used for the experiment. Three quality protein maize (ART/OB/98/SW6, OBA 98, ART/OB/98/SW1) were collected from the Institute of Agricultural Research and Training (IAR & T), Ibadan Nigeria. Cultivar 10–5–W was sourced from the National Centre for Genetic Resource and Biotechnology (NACGRAB), Ibadan, Nigeria, Cultivar 3–1–4 was obtained at Ado Ekiti, Nigeria, while Cultivar 10–1–Y was acquired at Ago Iwoye, Nigeria (Table 13).

 

 

Table 13 Sources and collection of maize cultivars

  

5.2 Source of ultraviolet radiation
The UV light source used was an UV lamp B (320 nm to 290 nm) at the Department of Physiotherapy, University College Hospital Ibadan, Nigeria. The seeds were spread in the Petri dishes and exposed to UV lamp at a distance of 22 m. The time of exposure was varied at intervals of 20 minutes. The treatments were; 0, 20, 40, 60, 80, 100 minutes, while 0 minute served as control.
 
5.3 Soil preparation
The polythene pots were filled with loam soil of 7 kg, and holes were punched at the bottom to allow aeration and drainage of excess water from the pot.
 
5.4 Experimental site and design
The experiment was conducted in screen house of the Department of Botany Nursery Farm, University of Ibadan. The site is situated within the tropical rain forest region of Nigeria (Latitude 70o 30’N, Longitude 30o 54’E). The polythene pots were arranged in a complete randomized design with three replications.
 
5.5 Planting and cultural practices
Two maize seeds per cultivar were planted per hole at the depth of 15cm. After two weeks, thinning of one plant per stand was applied. Weeding was conducted at weekly intervals, while watering was done at intervals of 3 days to field capacity.
 
5.6 Data collection
Data were collected on days to plant emergence, growth, yield, agronomic and mutation tolerance characters. Growth characters evaluated were: plant height, leaf length, leaf width, number of leaves, tasseling length and stem girth. Yield characters assessed were stover weight and grain weight per stand. Stover weight was determined using weighing balance, while total number of grains was estimated by visual counting of the grains. Agronomic characters include: plant stand, plant aspect, mutation tolerance, ear aspect, plant husk cover, ear harvest, plant harvest. Mutation tolerance scores ranges between 1 and 9. Highly tolerance to mutation scores from 1–3, moderately tolerant 4–6, while highly susceptible to mutation was scored 9. Other agronomic and drought tolerance characters ranged between 1 and 5, in which one is excellent, 2 is good, 3 is fairly good, 4 is fair, while 5 is poor.
 
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