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Abstract
Sugar Beet (Beta vulgaris L.) considered one of the most important crops grown for sugar production all over the world. This crop has been cultivated in Egypt as a commercial sugar crop since 1982 in Kafr EL-Sheikh. Now (2005) its plantation area covered the north and the northwest of Delta as well as the Middle and Upper Egypt. Sugar beet plant attacked by numerous diseases, among them the rust disease (Uromyces betae) considered the most important where caused high losses in number of plants and sugar production. The present work aimed to reduce these losses across several agricultural, biological and chemical practices. The obtained results could be summarized as follow:1-The infection with sugar beet rust disease (Uromyces betae kicx) was observed during fives successive seasons (1999-2003) in most surveyed governorates and during 1999 and 2001 seasons only in El-Faiyum governorate. The lowest and highest disease severity (DS) was recorded during seasons 2000 and 2001, respectively. DS was varied also between different surveyed govrnorates. Domyat governorate recorded the highest DS in most seasons followed by Kafr-El-Sheikh, Dakahliya, Gharbeia, Beheira and El-Faiyum, respectively. 2- Reactions of different plant species corn, garden rocket, faba bean, peanut, radish, soybean, spinach, swiss chard, table beet, turnip, fodder beet and sugar beet) against infection with U. betae were examined. Among all plant species, table beet, fodder beet and table beet only could be infected. 3- Isolates of U. betae collected from different localities were significantly varied in their pathogenic abilities. isolate (A) from Kafrsaad-Domyat was the most virulent followed by isolate (B) from El-Hamol-Kafr-El-Sheikh, (C) from Belkas-Dakahliya, (D) from Bassioun-Gharbiya and (E) from El-Rehmania-Beheira, respectively. 4- The virulence of the above-mentioned isolates was not alter by the used inoculation methods (brushing, spraying or dusting). Urediospores particularly those of isolate A were able to infect sugar beet leaves even after storage for more than 6 months under lab conditions. 5-Examination of the RAPD bands using three random primers revealed that the similarity between isolates A, B and C was greatly varied and this might interpreted the variation existed in their pathogenic ability. 6- The younger (30-60 days old) potted sugar beet plants were resistant against infection with any of the 5 rust isolates tested. The rust symptoms appeared and developed quickly on plants aged 90 and reached its maximum levels on plants aged 120 to 150 days then decline with increasing age to 180 days. 7- All sugar beet cultivars tested (10 cvs.) were susceptible, but to different extents, against infection with U. betae under greenhouse conditions. Based on number of pustule/leaf, these cultivars were categorized as follow. Less susceptible cvs (Farida, Gloria, Top and Toro), moderate susceptible cvs (Negma, Gazail and Pleno) and high susceptible cvs (Raspoly, Lola and Kawemira). 8- The fungicide Caramba was the best for controlling the artificial rust infection with (U. betae) followed by Emineat, Sum eight, Plantvax, Mpect, Saprol and Arvil, respectively. The rust infection on cv Farida sprayed with fungicides Caramba and Emineat (before or after inoculation) and cv. Raspoly sprayed with the fungicide Caramba (before inoculation only) was completely prevented.
1. Spraying with growth substance viz. IAA, NAA and GA3 (either before or after rust inoculation) significantly decreased rust infection comparing with the control (unsprayed). Efficacy of a known substance was significantly increased as its concentration (100-300ppm) increased. IAA at 300 ppm used before or after inoculation was the most effective in this respect.
2. Spraying with any plant extract (thyme, eucalyptus, black nightshade, christmas berry, garlic and Khella (tooth pick) at any concentration, either before or after inoculation, significantly decreased rust infection comparing with the control (unsprayed) treatment. Spraying before inoculation was more effective than after inoculation. Garlic extract at the highest concentration, was the best while extracts of Khella (pick tooth) was the least.
3. Phenol (free, conjugated and total) and amino acids content were higher in the rusted sugar beet leaves (U. betae) than the healthy one. The phenol content was higher in the LS (Farida and Gloria) than the HS cvs. (Raspoly and Lola), while the opposite was noticed concerning the amino acids content. Moreover, reduction in the amino acids content (due to artificial rust infection) was higher in the LS than the HS cvs.
4. Carbohydrates (total and insoluble) and sugars (total and reducing sugars) reduced in the artificially rusted leaves comparing with the healthy one and were lower in the LS than the HS cvs. Reduction in both parameters (due to rust infection) was greater in LS than HS cvs.
5. The photosynthetic leaf pigments (chlorophyll a and chlorophyll b and carotene), in general, were higher in the healthy leaves than in the infected one and in the LS than HS cvs. Reduction in the photosynthetic leaf pigments was higher in the HS than the LS cvs.
6. Activities of the oxidative enzymes (peroxidase, polyphenol-oxidase and catalase) were higher in rust-infected leaves than in the healthy leaves. Although activities of these enzymes were higher in the LS than HS cvs., the rate of increase in activities was higher in the HS cultivars than the LS ones.
7. The N, P and K contents were higher in healthy leaves than the rusted one and in the LS than the HS cvs. Thus, rust infection decreased N, P and K contents comparing with the healthy leaves. Reduction in these elements (due to infection) particularly P and K was lower in the LS than HS cvs.
8. The highest natural rust infection (disease severity) was recorded on sugar beet plants sown at mid-August followed by those planted at mid-September, mid-October and mid-November, respectively. In all plantations, the disease severity was sharply increased on 1st April and reaches its maximum records on 15th April of both 2001 & 2002 seasons. Disease severity was significantly lower on Farida (LS cv) than Raspoly (HS cv.).
9. from epidemiology view, the area under disease progress curve (AUDPC) was higher on the HS cv than the LS cv and on the early sowing (mid-August) than the late one (mid-November). However, rate of increase in disease/day (r-value) showed the same trend concerning cultivars but the opposite trend was noticed concerning sowing dates.
10. The reaction of tested sugar beet cultivars against the natural rust infection under field conditions was similar to their reactions under greenhouse conditions. Farida cv was the least susceptible followed by Gloria, Top, Toro, Negma, Gazail, Pleno, Kawemira, Lola and Raspoly cvs., respectively. The determined growth characters (dry matter, length, diameter, fresh and dry root weights of roots and shoot fresh weight), total soluble solids (TSS) and sucrose in roots as well as sucrose purity were correlated positively with cultivar resistance. Values of all parameters were higher in the healthy plants than the rusted one and in the less susceptible than the high susceptible cvs.
11. Efficiencies of tested fungicides viz. Caramba, Emineat, Sum eight, Plantvax, Impect, Saprol and Anvil for controlling rust infection under greenhouse (artificial infection) and field conditions (natural infection) were similar. The fungicide Caramba was best of all for suppressing the natural rust infection and improving root fresh weight, total soluble solids and sugars content in roots while Anvil and Saprol fungicides were the least effective in this respect. In all fungicidal treatments, the LS cv. Farida gave better results than the HS cv. Raspoly comparing each other or with their unsprayed control treatments.
12. Severity of the sugar beet rust disease was significantly increased while yield parameters (root yield, total soluble solids (TSS %) and sucrose content %) were significantly decreased by applying the narrower distance between rows (50cm) or plants (10cm) compared with wider distance between rows (60cm) and plants (20 & 30cm). Combining between wider row and planting distances resulted in the lowest DS and highest yield parameters in comparison with the narrower row and planting distances. This trend was true in both cultivars tested.
13. Rust severity was decreased while TSS % and sucrose content in roots were increased significantly by using the lower and middle levels of N fertilizer (60 and 80 kg/feddan) while the higher level (100 Kg/feddan) showed the opposite results comparing with unfertilized treatment. However, applying different levels of N and P fertilizers significantly increased root fresh weight compared with the unfertilized treatment. All determined parameters were significantly improved by applying P fertilizer (15 and 30 kg (P2O5)/feddan) comparing with the unfertilized treatment. Disease severity was lower while root fresh weight, TSS % and sucrose content were higher on cv. Farida than cv. Raspoly. Applying P (30kg) + N (80 kg) per feddan resulted in lowest DS and highest yield parameters for both cvs.
14. Intercropping sugar beet and faba been significantly increased disease severity as well as fresh weight of sugar beet roots in comparison with the sole sugar beet. Sugar beet intercropped with faba been at rate 3:1 and 1:3 (row/row) resulted in the highest increase in the disease severity and root fresh weight, respectively. On the contrary, total soluble solids (TSS %) and sucrose content in roots of the two tested sugar beet cultivars were significantly decreased by all tested intercropping treatments in comparison with the control (sugar beet alone). Intercropping the tow crops at rate 1:3 and 3:1 resulted in the highest decreases in both criteria, respectively.
15. Spraying with any plant extract tested (garlic, thyme, eucalyptas, black night shade, christmas barry tree and khella ”pick tooth”) significantly decreased DS and increased the root fresh weight, TSS % and sucrose content in sugar beet roots under field conditions during 2000 and 2001 seasons. In this respect, garlic extract was the best followed by thyme extract while extract of Khella (pick tooth) was the least effective compared with the control treatment.
16. Spraying with promoting growth substances tested significantly decreased DS and increased the root fresh weight (kg/plant), TSS % and sucrose content in sugar beet roots under field conditions during 2000 and 2001 seasons. In this respect, IAA was the most effective followed by NAA and GA3, respectively compared with the unsprayed control treatment.