APPLICATION OF SOME GROWTH REGULATORS ON POWDERY MILDEW DISEASE OF SUGAR BEET

APPLICATION OF SOME GROWTH REGULATORS ON POWDERY MILDEW DISEASE OF SUGAR BEET

El-Kady, M.S. and M.M.A. El-Mansoub

Sugar Crops. Res. Institute, Agri. Res. Center, Giza, Egypt.

Key Words:gibberellic acid, GA₃, indole acetic acid, IAA, naphthalene acetic acid, NAA, growth regulators, powdery mildew, sugar beet.

ABSTRACT

Powdery mildew is a fungal disease which causes a serious reduction in both root and sugar yields in sugar beet area in Al-Fayum.This study was carried out at El-Fayoum Governorate, (29°17ˋ N; 30°53ˋ E), Egypt, to study the effectof three growth regulators (gibberellic acid (GA₃), indole acetic acid (IAA) and naphthalene acetic acid (NAA)) at the levels of 0, 100, 200 and 300 ppm concentration on disease severity, growth, yield and quality of sugar beet plant during 2018/2019 and 2019/2020seasons.The results revealed thatthe application of GA₃ followed by NAA then IAA as growth regulators decreased disease severity% of powdery mildewand increased growth, yield and quality of sugar beet crop compared to control treatment. Increasing growth regulator concentrations from zero up to 100, 200 and 300 ppm decreaseddisease severity% and increased yield and quality traits of sugar beet crop in both seasons under study.

INTRODUCTION

Sugar beet (Beta vulgaris L.) is considered as one of the two important sugar crops worldwide. Total sugar beet cultivated area reached 208.33 thousand hectares in Egypt. Recently sugar beet surpassed sugar cane in sugar productivity and became the first source of sugar production in Egypt compared to sugar cane. Sugar beet is suffering from infection with many important plant diseases in various stages of development. Fungal diseases are the most important diseases that affect beet in terms of economic importance and spread.

Powdery mildew (Erysiphebetae) of sugar beet is a serious fungal foliar disease resulting in sugar yield losses of up to 30%. The disease appears first on lower and older leaves and gradually spreads towards the upper and younger leaves. It is characterized by the formation of white, later grey, tan mildew areas on both sides of the leaf. In general, infection is more common on upper surface of leaves. Severely affected leaves turn yellow and ultimately dry up, (Srivastava, 2004). Powdery mildew of sugar beet is an important disease in several sugar beet growing countries caused by Erysiphebetae(Vanha) show declining rates of net photosynthesis as the disease develops; relative to healthy controls, (Hills et al., 1980).In recent years, powdery mildew in sugar beet began to spread in Egypt and became economically worthwhile. The infection appears in March and continues in April and May and appears as a shiny layer like flour on the surface of the leaf. The disease is almost widespread in sugar beet production areas in Egypt, and it acts at the time when sugar beet is synthesizing sugar and accumulating it. The disease reduced the root yield by 20-25% and has been found to be the main cause for low production of sugar (Karve, et al., 1973). If the disease is not controlled, 20 to 35% loss in sugar yield can occur (Draycott, 2006). The reduction ofroot yield may exceed 22% and root sucrose content may exceed 13% (Forster, 1979).Growers typically mange powdery mildew by integrating rotation with non-hosts crops including corn, soybean and wheat, planting powdery mildew tolerant varieties, and could be controlled by foliar spraying with different fungicides (Ata, 2005),andplant growth regulators (Moustafa, et al.,200l bandEl-Taweelet al., 2004). 

On the other hand, plant growth regulators are widely used in agriculture to increase plant growth and production. There are different growth regulators that manifest physiological effects on crop growth, morphological development and improve yield under marginal conditions. The commonly used class of plant growth regulators includes plant growth hormones such as auxins(indole acetic acid and naphthalene acetic acid) and gibberellic acid (Fukao and Bailey-Serres, 2008).

Gibberellic acid, also called Gibberellin A₃, GA or GA₃, is a very potent hormone whose natural occurrence in plants controls their development. Gibberellins involved in a number of cellular processes that regulate seed germination and growth of aerial plant parts, including floral induction and fruit development (Spaepenet al., 2009). It is an established phytohormone used commercially for improving the productivity and quality of a number of crop plants (Silva et al., 2013).Gibberellic acid has the ability of modifying the growth pattern by affecting the cell elongation and cell division, biosynthesis of enzymes, protein, and carbohydrates contents (Gupta and Chakrabarty, 2013 and Milne et al., 2013). The application of plant growth regulators (GA₃) can be useful not only to achieve the technological quality desired by the ethanol industry, but the quality needed for other purposes as forage (Almodareset al., 2013).GA₃is compound able to change the morphology and physiology of plants and can be applied at different times (Leiteet al., 2011), depending on the grower purpose for the crop.

Auxins like, indole acetic acid (IAA) plays a main role in maintaining plant growth under normal or stress conditions. IAA in sugar beet is used to improve biological values of seed and development of the vegetation to increase the yield of roots and sugar production (Ahmad et al., 2005).Also, naphthalene acetic acid (NAA) is a synthetic plant hormone in the auxin family and is an ingredient in many commercial plant rooting horticultural products; it is a rooting agent and used for the vegetative propagation of plants from stem and leaf cuttings(Morikawa and Takahashi, 2004). Therefore, spraying sugar beet plants with auxins may be occasion the balance between foliage growth and sucrose content in roots. indoleand naphthalene acetic acid are growth regulators that has been widely used to reduce vegetative growth to allow plants to direct more metabolic energy towards the productive structure (Fletcher et al., 1994), also it inhibits the synthesis of the plant hormone gibberellic acid which plays a major role in enhancing vegetative growth (Wahdan, 1990 andMahmoudet al., 1994).

Therefore, this investigation aims to study the effect of growth regulators (gibberellic acid, indole acetic acid and naphthalene acetic acid)at0, 100, 200 and 300 ppm concentration on disease severity, growth, yield and quality of sugar beet plant at El-Fayoum Governorate.

MATERIALS AND METHODS

The experiment was carried out atEl-Fayoum Governorate, (29°17ˋ N; 30°53ˋ E), Egypt, to study the effectof three growth regulators (gibberellic acid (GA₃), indole acetic acid (IAA) and naphthalene acetic acid (NAA)) at 0, 100, 200 and 300 ppm concentration on disease severity, yield and quality of sugar beet plant during the two successive seasons of 2018/2019 and 2019/2020. The experimental site has the following characteristics: The average mean temperature is 36.4 Cº in the hottest month (July) and 11.4 Cº in the coldest month (January). Annual mean relative humidity is 45%. The soil texture was siltyclay soil (40% clay, 40% silt and 20% sand) with bulk density 1.78gm/m³. Sugar beet multi-germ variety named "Farida" wassown on the first of October and harvest at 210 days age in both seasons. Surface irrigation was used in the experiment. Nitrogen was added in the form of ammonium nitrate (33.5% N) at a rate of 100 kg N/fed in three equal splits, the first was applied after thinning at 4-leaf stage and other splits were added after every three week later. Phosphorous in the form of super phosphate (15.5%) at a rate of 30 kg P₂O₅/fed were added during land preparation. Potassium in the form of potassium sulfate (48%) was added at the rate of 48 kg K₂O/fed with the last dose of nitrogen. Other culture practices treatments, were applied as recommended by the Sugar Crops Research Institute (SCRI) recommendation.

The experiment was set up in split plot design with 12 treatments and three replicates. The experimental unit’s area was 12 m² (5 ridges, 4 m long and 60 cm apart). Sugar beet seeds were sown on hills spaced 20 cm. The main plots of the experiment were occupied by three growth regulators (gibberellic acid (GA₃), indole acetic acid (IAA) and naphthalene acetic acid (NAA)) and four concentrations of growth regulators treatments (0, 100, 200 and 300 ppm) were distributed at random within the main plots and applied. Growth regulators under study were applied in two equal splits after 60 and 75 days from planting.

Disease assessment:

When the severity of the disease reached its maximum, the recording was conducted to determine the extent of the infestation. For determination of infestation percentage and selection of healthy plants, the index suggested by Paulus et al. (2001) was used which is the latest index used powdery mildew (Erysiphebetae). Determination of disease assessment at four months from sowing, powdery mildew was counted on 100 plants and disease severity was calculated according to the scale of Whitney et al., (1983). The infestation score of 0-5 was attributed to the leaves based on 10, 35, 65, 90 and 100% infestation.For each treatment in each replication, 100 leaves were recorded and the infestation score was attributed. Scale ranged from 0-5, categories whereas 0= no mildew colonies observed 1=1-10%, 2=11- 35%, 3=36-65%, 4=65-90% and 5=91-100%, respectively of matured leaf area covered by mildew and the average disease rating per treatment was calculated.

Disease severity (%) =

The percentage of treatment efficiency in the reduction of powdery mildew severity was calculated using last equation.

Determination of total free amino acids

Total free amino acids content was estimated according to the methoddescribed by Yemmet al. (1955).

Determination of total phenolic compounds:

Total and free phenol compounds were determined in the treated infected plants with the tested fungicides using UV/Vis. Spectrophotometer, Jenway England at wave length 750 nm as described by Singleton et al (1999) was determined England (Folin and Ciocalteau phenol reagent).

Determination of total chlorophyll:

            Total chlorophyll content of leaves was measured as optical density (OD) using Chlorophyll meter Model (SPAD-502).

Randomly, five plants in the three guarded central rows of each plot were harvested to estimate the following traits:

Productivity traits

1. Root yield (ton/fed): calculated from root weight of experimental unit.
2. Top yield (ton/fed): calculated from top weight of experimental unit.
3. Sugar yield (ton/fed): calculated according to the following equation: Sugar yield (ton/fed) = extractable sugar(ES) % × root yield (ton/fed)/100

Quality traits

Quality traits (Sucrose %, Impurities of juice, (K and Na) andAlpha-amino-N concentrations) weredetermined in El-Fayoum sugar company laboratories to asses:

1. Sucrose loss to molasses (SLM %) was determined according to (Devillers, 1988).
2. Extractable Sugar (ES) %=Sucrose % – SLM% - 0.6 (Dexter et al., 1967).
3. Extractability = (ES% / Sucrose %) × 100

Statistical analysis

Data collected of each season and each location was statistically analyzed according to Gomez and Gomez (1984) by using SAS computer software package. The separate analysis of variance for each experiment (location), and then the combined analysis of variance for different characters were performed on plot mean basis. Revised L.S.D at 5% level was used to compare the means according to Waller and Duncan (1969).

RESULT AND DISCUSSIONS

Severity percentage:

Data illustrated in Table 1 showed that, a significant decrease in disease severity percentage under application of gibberellic acid (GA₃) compared toindole acetic acid (IAA) and naphthalene acetic acid (NAA), and this decrease amounted to (1.86 and 1.31%) and (2.23 and 1.09 %) in 1^st and 2^nd seasons, respectively. as well as, severity % significantly decreased by increasing concentration of growth regulators under study from 0 up to 300 ppm by 4.47% in both seasons. Also, the interaction between growth regulators types and concentrations was significant as shown in Table 1, where the lowest severity percentage was gained under the application of300 ppm of gibberellic acid (GA₃) amounted to 8.55 and 7.69 % in 2018/19 and 2019/20 seasons, respectively.

El-Fikiet al. (2007) indicate that spraying plants of sugar beets with Indole acetic acid (IAA), naphthalene acetic acid (NAA) and gibberellic acid GA₃comparing with the control was significantly effective for powdery mildew in sugar beet. Also, the disease severity was minimized by spraying plants with GA₃ (300ppm) after 70 days from sowing. In fact, some important metabolic activities might be changed due to applying the tested growth regulators. Saswatiet al. (1988) found that, the pretreated rice plants with GA₃ exhibited induced resistance to rice sheath rot disease. EI-Nagar (1998) indicated that the phenolic compounds, especially the total phenols were more increased in the stem rust infected wheat plants pretreated with different concentrations of GA₃, as compared with the infected, untreated plants.

Table (1). Effect of growth regulators at different levels on disease severity (DS) % of sugar beet in 2018/19 and 2019/20 seasons.

A: Growth regulators                                         B: Concentrations      

Total chlorophyll

A significant effect of growth regulators was observed on total chlorophyll as shown in Table (2).Three growth regulatorsunder studysignificantly increased total chlorophyll,GA₃showed superior performance, followed by NAAthenIAA in both seasons.Also, total chlorophyll significantly increased by increasing the concentration of growth regulators from zero up to 200 ppm, the increases were 8.94% and 14.47% for the levels of 100 and 200 ppm in the first season and 5.97% and 6.70% in the second season as compared with control.Results of the interaction between growth regulators types and concentrations showed that total chlorophyllunder 300 ppm of GA₃was observed to be significantly higher than other treatments in both seasons.

Qotob, et al., (2019) revealed that the foliar application of plant growth regulators(gibberellin) increased the pigment content i.e. chlorophyll-a; chlorophyll-b andcarotenoids. Application of gibberellins has shown enhanced activities of carbonic anhydrase, nitrate reductase (Afrozet al., 2005), CO₂ fixation, stomatal conductance (Bishnoi and Krishnamoorthy, 1991) and ribulose^-1,5-biphosphate carboxylase/oxygenase (Yuan and Xu, 2001). GA₃ alters membrane permeability to ions (Gilroy and Jones, 1992) and improves translocation potential to the sink (Peretó and Beltrán, 1987). Also, Azab, (2018)Found that increasing levels of GA₃ enhanced the levels of photosynthetic pigments. These results were coordinated with Shaddadet al. (2013) who obvious that GA₃ treatments improved the photosynthetic pigments and consequently the crop yield of two wheats cultivars. In addition, Shreelalithaet al. (2015) found that the GA₃ acid enhanced the carotenoids in the corn plants. Using of plant growth regulators as GA₃stimulate increasing synthesis of photosynthetic pigments (SalehiSardoei, 2014).GA₃ increases the chlorophyll concentrations in leaves by increasing the numbers and sizes of chloroplasts and enhances the ultra-structural morphogenesis of plastids (Gilroy and Jones, 1992).

Total free amino acid

Table (2) indicated that, GA₃ in the first season and NAA in the second season were significantly more efficient on total free amino acid compared to IAA.Sprayed sugar beet plants by 100 to 300 ppm of growth regulators significantly increased total free amino acid, the levels at 200 ppm was the best treatment, where it gave the highest value of total amino acids (2.04 and 1.95%) in the both seasoned. The interaction between types and concentrations of growth regulators under study was significant on total free amino acid as illustrated in Table (2), where, the highest value was noticed under the application of 200 ppm of gibberellic acid (GA₃) compared to other applications in both seasons.Proline, a multifunctional amino acid, besides acting as an excellent osmolyte is also known for stabilizing subcellular structures such as proteins and cell membranes, scavenging free radicals, balancing cellular homeostasis and signaling events and buffering redox potential under stress conditions (Hayat et al., 2012).

Table (2). Effect of growth regulators at different levels on total chlorophyll and free amino acids of sugar beet in 2018/19 and 2019/20 seasons.

A: Growth regulators                                        B: Concentrations

Phenols

Resulted as illustrated in Table (3), revealed that sprayed sugar beet plants with GA₃, NAA or IAA significantly increased free, conjugated and total phenols as compared to control (zero growth regulator), it is imported to note that GA₃ was the best treatment compared to NAA or IAA.The increases of total phenols when used GA₃ were (1.76% and 5.35%) and (2.43% and 5.61%) over NAA and IAAin the first and second seasons, respectively.

Data also found that application of growth regulator at level 300 ppm gave the highest phenols compared to 100 or 200 ppm in both seasons. As example, growth regulators at 300 ppm led to increase free phenols by 14.36 and 17.05% as compared to control in both seasons, respectively. The interaction between different types and concentrations of growth regulators under study was significant on free, conjugated and total phenolsin both seasons as shown in Table (3). Where, the application of 300 ppm of gibberellic acid was the more efficient on all measurements of phenols compared to control as well as 100 and 200 ppm concentrations in both seasons. EI-Nagar (1998) indicated that the phenolic compounds, especially the total phenols were more increased in the stem rust infected wheat plants pretreated with different concentrations of GA₃, as compared with the infected, untreated plants.

Yields

Data in Table (4) revealed that sugar beet sprayed by GA₃ compound significantly recorded higher values of root, top and sugar yields (ton/fed) in the 1^st and 2^nd seasons, compared to beets sprayed by  auxins compounds (NAA or IAA). Applying GA₃ resulted in producing 0.43, 0.35 and 0.26 tons of roots, top and sugar per fed, respectively higher than that attained in case of using NAA. Moreover, the same traits recorded 1.11, 0.95 and 0.5 tons of roots, top and sugar/fed, successively when GA₃ was used, in comparison with IAA, in the 2^nd season. Results in Table (4) cleared that increasing growth regulator concentrations from zero up to 100, 200 or 300 ppm had a positive impact on the values of root, top and sugar yield during both seasons. Meantime, raising the level of the applied growth regulator to 200 ppm resulted in higher values of sugar yield by 0.55 and 0.99 ton/fed compared to control treatment in 1^st and 2^nd seasons, respectively.

Root, top and sugar yield/fed (ton) was significantly influenced by the interaction between types and concentrations of growth regulators under study in two seasons. Where, the application of 300 ppm of GA₃ gave the highest significant value of root yield in both season and top yield in first season only. While, the application of 200 ppm of GA₃ gave the highest significant value of sugar yield in both seasons and top yield in second season.

Table(3). Effect of growth regulators at different levels on phenols (free, conjugated and total) of sugar beet in 2018/19 and 2019/20 seasons.

A: Growth regulators                                                                                                               B: Concentrations      

Table (4). Effect of growth regulators at different levels on top, root and sugar yield (ton/fed) of sugar beet in 2018/19 and 2019/20 seasons.

A: Growth regulators                                                                                                                     B: Concentrations                          

In general, photosynthetic efficiency increases along w ith the chlorophyll concentration. Thus, GA₃ in directly causes the increase in chlorophyll (Ashraf and Iram, 2002) that resulted in the accumulation of more dry mass (Khan, 1996). In addition, GA₃ caused the increase in the endogenous Indole acetic acid contents (Reid and Davies, 1992). Also, Sun Physiologically, a major function of GA₃ in higher plants can be generalized as stimulating organ growth through enhancement of cell elongation and, in some cases, cell division. In addition, Gas promotes certain developmental switches, such as between seed dormancy and germination, juvenile and adult growth phases, and vegetative and reproductive development. El-Fikiet al. (2007) indicate that spraying plants of sugar beets with Indole acetic acid (IAA), naphthalene acetic acid (NAA) and gibberellic acid GA₃ comparing with the control significantly increased fresh weight of sugar beet roots (ton/fed). Also, Asilet al., (2011) indicated drenching with gibberellin increased the floral stalk height as compared to the control. It may be attributed to the effect of gibberellin in stimulating and accelerating cell division, increasing cell elongation and enlargement, or both (Hartmann and Kester, 1963). Abd El-Kader (2011) indicated that spraying sugar beet plants by indole acetic acid at the concentration of 200 ppm gave the highest values of top yield/fed (5.75 and 5.86) and root yield/fed (27.65 and 28.28 tons) in first and second seasons, respectively. The increase in root yield due to increasing Indole acetic acid (IAA) concentration may be attributed to IAA stimulated vegetative growth and increased nitrogen fertilizer which caused increased leaf area index and raising photosynthetic rate which led to increasing root yield per fed. Also, Azab, (2018) found that increasing of GA₃ level from 50 to 150mg/L GA₃ gave significant increment of root yield/fad compared with control.

Quality

Data presented in Table (5) showed that all growth regulators types under study significantly effected on quality traits, i.e. sugar lose to molasses, extractable sugar and extractability percentages in both seasons. Gibberellic acid (GA₃) produced 0.36 and 0.5% higher sugar lost to molasses in the 1^st and 2^nd seasons respectively, and 1.03 and 0.96 %  higher extractable sugar % in the 1^st and 2^nd season, respectively, and finally 0.63% higher extractability % in the 1^st season compared to the indole acetic acid (IAA). In the same time, naphthalene acetic acid (NAA) treatment recorded the highest extractability (88.84%) in the 2^nd season. On the other hand, application of 200 ppm of growth regulators under study recoded maximum sugar lost to molasses (4.49 and 5.08 %) compared toother concentrations in the 1^st and 2^nd seasons, respectively. while, the application of 300 ppm concentration increased extractable sugar (15.25 and 15.96%) and extractability (89.58 and 89.38%) in the first and second seasons, respectively.The interaction between different growth regulators under study and it concentration's was significant on sugar lose to molasses, extractable sugar and extractability percentages (Table 5). Where, the highest values of quality traits was gained under application of GA₃ compound with 200 ppm on sugar lost to molasses and extractable sugar percentages, and 300 ppm on extractability percentages.

Table (5). Effect of growth regulators at different levels on sugar lost to molasses, extractable sugar and extractability % of sugar beet in 2018/19 and 2019/20 seasons.

A: Growth regulators                                                                                                               B: Concentrations