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Susceptibility of Orobanche ramosa and potato tolerance to rimsulfuron
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Crop Protection 24 (2005) 7–13 www.elsevier.com/locate/cropro
Susceptibility of Orobanche ramosa and potato tolerance to rimsulfuron M.A. Haidar, N. Iskandarani, M.M. Sidahmed, R. Darwish American University of Beirut, Faculty of Agricultural and Food Sciences, Riad-El-Solh, Beirut 1107 2020, Lebanon Received 11 May 2004; received in revised form 26 May 2004; accepted 1 June 2004
Abstract Field studies were conducted in Lebanon to examine Orobanche ramosa control, and the tolerance of six potato cultivars, to single or repeated foliar application of rimsulfuron. The effect of rimsulfuron was evaluated on a potato cultivar ‘‘Spunta’’ in 2000 and 2001, and on five new potato cultivars ‘‘Columbus’’, ‘‘Farmer’’, ‘‘Recolta’’, ‘‘Score’’ and ‘‘Timate’’ in 2001. The results indicate that both single and sequential applications of rimsulfuron between 20 and 50 g ai/ha significantly reduced Orobanche shoot number and dry weight compared to the control. Repeated applications (three times) was the most effective in reducing Orobanche shoot dry weight in all tested cultivars in comparison to their respective controls. Total potato yield within a cultivar was not reduced by single or sequential application of rimsulfuron, but marketable yield and tuber quality were significantly reduced in all cultivars (except for Score and Timate). Most tubers were small, fissured, and had a high incidence of malformed popcorn-like tubers. The most susceptible cultivars to Orobanche and sensitive to rimsulfuron were Spunta, followed by Recolta, Columbus, Farmer, Score and then Timate. Single or sequential application of rimsulfuron at 20 g ai/ha could be used to control Orobanche in Timate and Score cultivars. Although both varieties were slightly susceptible to repeated application of rimsulfuron, total and marketable yield was not affected. Additional research is required under different locations in Lebanon before a recommendation to growers for the use of rimsulfuron can be made. r 2004 Elsevier Ltd. All rights reserved. Keywords: Application timings; Lebanon; Cultivars
1. Introduction Orobanche ramosa Forsk (Branched broomrape) is a root-parasitic flowering plant in the family Orobanchaceae (Mitich, 1993). It parasitizes roots of a variety of herbaceous dicots, where it develops a physiological connection with the host xylem and phloem. O. ramosa is endemic in the Middle East and constitutes one of the most severe constraints to potato production in the region (Goldwasser et al., 2001; Haidar et al., 2003; Parker and Riches, 1993). Corresponding author. Department of Plant Sciences, American University of Beirut, FAFS, Riad El-Solh, Beirut 1107 2020, Lebanon. Tel.: +961-1-350000; fax: +961-1-74460. E-mail address: [email protected] (M.A. Haidar).
0261-2194/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.cropro.2004.06.007
Potato is one of the most important and widely grown crops in the Mediterranean region. Approximately 100,000 ha of potatoes are grown annually in Lebanon. Spunta is the most widely grown potato cultivar in Lebanon, but is highly susceptible to and damaged by O. ramosa (Haidar and Bibi, 1995). It is estimated that over 90% of the irrigated potato Spunta fields are parasitized by O. ramosa causing severe yield quantity and quality losses (Haidar, personal communication). Farmers are concerned about losses caused by this parasite and are seeking ways to control it. Currently, there are neither pre-emergence nor post-emergence (POST) herbicides, which control Orobanche in potato. Farmers rely on hand pulling and soil sterilization with highly volatile compounds for controlling Orobanche. These methods are expensive, injurious to the crop and
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cannot be applied economically on a large scale. Therefore, the search for new methods for controlling Orobanche has become increasingly important. Rimsulfuron is a POST sulfonylurea herbicide used for controlling many grasses and broadleaved weeds in field corn (Mekki and Leroux, 1994; O’sullivan et al., 1998), potato (Ackley et al., 1996; Blackshaw et al., 1995; Eberlein et al., 1994; Robinson et al., 1996) and tomato (Ackley et al., 1997; Mullen et al., 2001). Sequential application of rimsulfuron was also found effective in controlling O. aegyptiaca or O. ramosa in tomato (Hershenhorn et al., 1998; Kleifeld et al., 1994) and potato (Goldwasser et al., 2001; Haidar and Sidahmed, 2000). However, little is known about its efficacy and selectivity under Lebanese irrigated field conditions, although deformed potato tubers of the standard potato cultivar ‘‘Spunta’’ were observed following rimsulfuron application (Haidar and Sidahmed, 2000). Thus, more information is required about its efficacy against Orobanche and selectivity of potato cultivars to rimsulfuron. Studies were initiated to determine (a) rimsulfuron doses and time of application required to control O. ramosa, and (b) the response of six potato cultivars to rimsulfuron.
2. Materials and methods 2.1. General experimental procedures Experiments were conducted in a field naturally infested with O. ramosa at the Agricultural Research and Education Center (AREC) of the American University of Beirut, Lebanon in 2000 and 2001. The AREC is located in the Northern Central Beqa’a plain of Lebanon. The soil was silty clay loam with a pH of 7.41, EC 0.24 ms/cm and 2.4% organic matter. In both years, all plots were tilled twice with a mouldboard, disked and levelled 2 weeks prior to planting. The experimental area received a uniform application of 2.5 t/ha of NPK (17:17:17) before disking each year. Nitrogen was applied 40 days after planting at a rate of 300 kg/ha each year. Plots were sprinkler irrigated every 8 days. The standard potato cultivar Spunta was planted on April 25, 2000, while five new potato cultivars Columbus, Farmer, Recolta, Score and Timate (Nederlandse Algemene Keuringsdienst-NAK) were planted on April 13, 2001. In both years, tuber pieces of potato cultivars were planted at 3.0 t/ha in the same field but at different spots. Plots (5 m long and 2.2 m wide) were hilled 6 weeks after planting (standard practice by Lebanese farmers). Potato rows were 0.7 m apart and within-therow spacing was around 0.35 m. To eliminate all weeds other than Orobanche, the entire experimental area received a standard application of metribuzin (SencorR,
70%) at 0.65 kg ai/ha 1 week after sowing each year. It is worth mentioning that metribuzin is widely used by Lebanese potato growers and is known to be safe when applied to potato. Rimsulfuron (Technical grade, 75% DF, from Dupont) was applied POST with a CO2-pressurized backpack sprayer that delivered 310 l/ha at 138 kPa through a Teejet 8002 flat fan spray tips. In 2000, rimsulfuron was applied at 10, 20, 30, 40 and 50 g ai/ha, while in 2001 rimsulfuron was applied at a single dose of 20 g ai/ha. Each dose was tested for single and repeated (twice or three times) application at 20, 40 and 60 days after potato emergence (DAPE). Plots were irrigated 2 days after each spraying. Potato plants were 8–12 cm tall at 20 DAPE. Nonionic surfactant (X-77) at 0.2%(v/v) was added to the spray solution. 2.2. Experimental measurements and statistical analyses Experimental plots (3 rows/plot) were arranged in a factorial randomized complete block design with five replications. Factors evaluated were rimsulfuron doses, application timing (20, 40 and 60 DAPE) and potato cultivars. Statistical analysis was done separately for the 2000 and 2001 data. All data were subjected to analysis of variance and Fisher’s protected least significant difference (LSD) test at p ¼ 0:05 level of probability was used to determine significant differences between treatment means. Orobanche data included Orobanche shoot number (75 and 90 DAPE) and shoot dry weight per 2 m2. Potato data included phytotoxicity visual rating (40, 60 and 90 DAPE), number of shoots of the middle row (40 DAPE), height (90 DAPE, 5 plants/ plot), total yield and tuber number of marketable and non-marketable yield. Potato yield was determined by harvesting the middle row (3.5 m2) in each plot. Yield quality was determined by separating harvested tubers into two classes: marketable (45:0 cm in diameter) and non-marketable tubers (o5:0 cm in diameter) according to Robinson et al. (1996).
3. Results and discussion 3.1. Orobanche management in 2000 Single or repeated application of rimsulfuron at all tested doses delayed the appearance and emergence of Orobanche shoots 75 DAPE as compared to the control (Table 1). Except for a single application of rimsulfuron at 10 g ai/ha, all tested doses significantly reduced Orobanche shoot number in Spunta 90 DAPE and shoot dry weight compared to the control. Rimsulfuron at 20 g ai/ha reduced Orobanche infestation by 94% when applied twice (20 and 40 DAPE) and 98.5% when applied three times (20, 40 and 60 DAPE). The greatest
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Table 1 Effect of rimsulfuron on average Orobanche shoot count and weight per 2 m2 in 2000a
Table 2 Effect of rimsulfuron (20 g ai/ha) on average Orobanche shoot count and dry weight per 2 m2 in 2001a
Rimsulfuron dose (g ai/ha)
Potato cultivar
Application time (DAPE)
10 20 30 40 50
20 20 20 20 20
10 20 30 40 50
20/40 20/40 20/40 20/40 20/40
10 20 30 40 50 Control
20/40/60 20/40/60 20/40/60 20/40/60 20/40/60 —
Shoot number
Shoot dry wt. (g)
75
90
53b 1c 0c 13c 0c
119ab 56b–d 29cd 84bc 36cd
61a 36b 15bc 20bc 17bc
0c 0c 0c 0c 0c
32cd 12cd 3d 0d 3d
12c 5c 1c 0c 1c
0c 0c 0 0c 0c 96a
5.7d 2.9d 0d 0d 0d 194a
3c 1c 0c 0c 0c 740a
reduction in shoot number and dry weight were recorded with repeated application (two or three times) of rimsulfuron at all tested doses (Table 1). Three sequential applications of rimsulfuron at 12.5 or 25 g/ha significantly reduced O. aegyptiaca infestation in potato (Goldwasser et al., 2001).
Shoot number (DAPE) 75
90
Shoot dry wt. (g)
Columbus
Control 20 20/40 20/40/60
213c 56ef 34ef 12f
174d 78fg 38g 38g
193d 91f–h 73gh 57gh
Farmer
Control 20 20/40 20/40/60
174cd 33ef 16f 22ef
297b 123de 115ef 36g
214d 154d–f 163de 64gh
Recolta
Control 20 20/40 20/40/60
324b 99de 39ef 52ef
285c 193d 98ef 70fg
271cd 207d 198d 112e–g
Score
Control 20 20/40 20/40/60
207c 46ef 25ef 32ef
286c 82fg 44g 36g
200d 85fg 40h 47h
Timate
Control 20 20/40 20/40/60
154cd 18f 22ef 15f
176d 66fg 80fg 29g
163de 91f–h 65gh 24h
Spunta
Control 20 20/40 20/40/60
440a 102de 45ef 52ef
400a 280c 142de 96ef
423a 328bc 323bc 271cd
a
Means followed by the same letter, within each column, do not significantly differ at the 5% level according to the LSD test.
Application time (DAPE)
a
Means followed by the same letter, within each column, do not significantly differ at the 5% level according to the LSD test.
3.2. Orobanche management in 2001 Single or repeated application of rimsulfuron at 20 g ai/ha significantly reduced Orobanche shoot number after 75 and 90 DAPE in all potato cultivars in comparison to their respective controls (Table 2). Repeated application of rimsulfuron (three times) was the most effective treatment in reducing Orobanche shoot dry weight in all tested cultivars in comparison to their respective controls. Our results suggest that Spunta is the most susceptible potato cultivar to O. ramosa. The highest Orobanche shoot count recorded was in the control treatment of Spunta in comparison to the controls of all cultivars. Cultivar susceptibility to O. ramosa ranged from very sensitive (Spunta, and Recolta), to sensitive (Timate and Score), with Columbus and Farmer cultivars showing moderate sensitivity. 3.3. Potato biomass and yield in 2000 Single or repeated application of rimsulfuron at 30 g ai/ha or above was toxic to Spunta early in the season (after 40 DAPE). Visual potato injury appeared 8 days after first spraying and included small leaves, purple venation of leaves, plant stunting and compact potato
plants, compared to the control (Table 3). Potato injury was similar to that in other studies (Blackshaw et al., 1995; Eberlein et al., 1994). No crop injury was observed later in the season (after 60 and 90 DAPE). Eberlein et al. (1994) observed visual injury on potato plants 1 week after spraying rimsulfuron at 15–70 g/ha, but disappeared later in the season. Rimsulfuron at all doses had no significant effect on potato plant number. However, single or repeated applications at 20 g ai/ha and above significantly reduced potato shoot height. The highest reduction in potato height was observed with repeated application of rimsulfuron at 40–50 g ai/ha (Table 3). All doses of rimsulfuron slowed down potato growth and delayed crop maturity. Our observations were similar to those of Mullen et al. (2001), that rimsulfuron delayed the maturity of tomato plants. Single or repeated application of rimsulfuron between 10 and 30 g ai/ha significantly increased total yield of Spunta, but reduced marketable yield (Table 4). All doses of rimsulfuron produced non-marketable potato tubers. Phytotoxicity was mostly reflected in the tuber quality of potato yield grown for fresh market with a high incidence of deformed and small tubers (Fig. 1).
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Table 3 Response of potato cultivar ‘‘Spunta’’ to rimsulfuron in 2000a Rimsulfuron dose (g ai/ha)
Application time (DAPE)
Phytotoxicity visual rating (%) (DAPE) b
40
60
90
Plant no.per row
Plant ht. (cm)
10 20 30 40 50
20 20 20 20 20
8a 8a 6ab 6ab 6ab
9a 8a 9a 8a 9a
9a 8a 9a 8a 9a
16a 16a 17a 16a 17a
49.5ab 44.5b–d 49.5ab 45.8b–d 44.3b–d
10 20 30 40 50
20/40 20/40 20/40 20/40 20/40
8a 8a 6ab 6ab 6ab
9a 8a 7ab 7ab 7ab
9a 8a 8a 8a 6ab
16a 17a 17a 18a 16a
49.3a–c 45.8b–d 41.8b–d 38.5d 40.3cd
10 20 30 40 50 Control
20/40/60 20/40/60 20/40/60 20/40/60 20/40/60 —
8a 8a 8a 6ab 6ab 9a
8a 8a 8a 8a 8a 9a
8a 8a 8a 8a 8a 9a
17a 17a 18a 16a 16a 16a
48.3ab 45.5b–d 42.3b–d 39.8d 41.3b–d 56.3a
a
Means followed by the same letter, within each column, do not significantly differ at the 5% level according to the LSD test. Scale (0–10), with 0 indicating complete death and 10 no injury.
b
Table 4 Yield response of potato cultivar ‘‘Spunta’’ to rimsulfuron in 2000a Rimsulfuron dose (g ai/ha)
Application time (DAPE)
Total yield (kg/3.5 m2)
Tuber number (no./3.5 m2) Marketable
Non-marketable
10 20 30 40 50
20 20 20 20 20
10.6b 9.5b 9.9b 7.4a 7.2a
0.2a 0.3a 0.3a 0.5a 0.1a
101ab 103ab 120a 72bc 81ab
10 20 30 40 50
20/40 20/40 20/40 20/40 20/40
10.9bc 11.1bc 8.5b 7.1a 7.4a
0.2a 0.0a 0.2a 0.0a 0.1a
52bc 79bc 66bc 48c 53bc
10 20 30 40 50 Control
20/40/60 20/40/60 20/40/60 20/40/60 20/40/60 —
10.4b 9.0b 8.5b 5.9a 7.1a 7.2a
0.1a 0.2a 0.2a 0.0a 0.0a 0.4a
130a 110a 45c 53bc 71bc 51bc
a
Means followed by the same letter, within each column, do not significantly differ at the 5% level according to the LSD test.
Although potato tubers were small and deformed, the significance difference in total yield compared to the control (Table 4) was due to the increase in the number of non-marketable tubers. The rate of deformed tubers increased with rimsulfuron dose and application time. Although repeated application of rimsulfuron was very effective in reducing Orobanche infestation, potato yield was severely damaged. Previous studies by Goldwasser
et al. (2001) and Eberlein et al. (1994) indicated that rimsulfuron at 15–70 g/ha was not toxic to potato, but our results suggest that repeated application of rimsulfuron at 10–50 g ai/ha significantly reduced marketable potato yield and tuber quality. Potato producers should be aware that repeated application of rimsulfuron at 10–50 g ai/ha can delay crop maturity and reduce crop quality of the cultivar Spunta.
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3.4. Potato biomass and yield in 2001
(b)
(a)
11
Results in Table 5 indicate that single or repeated application of rimsulfuron were not phytotoxic to all cultivars with respect to crop vigor, stand and number of plants in comparison to their respective controls. Also, plant height within a cultivar was not significantly affected by single or repeated application of rimsulfuron. Significant differences were found in potato yield between different treatments and cultivars. The lowest yield obtained was in Spunta, which was significantly lower than the other cultivars (Table 6). The highest total yielding cultivar was Columbus, with the repeated application of rimsulfuron (three times) yielding the highest, although it is not significantly different from other treatments. The second highest yielding cultivars were Timate or Score, where the highest yield was obtained with single or repeated application of rimsulfuron. Columbus, Farmer, Recolta and Score showed no significant differences between the different treatments. Applying Rimsulfuron once or twice significantly increased the total potato yield of Timate in comparison to the control. Applying rimsulfuron three times to Spunta gave the highest non-marketable potato yield, which was significantly different from the control as well
(c)
Fig. 1. Deformed potato ‘‘Spunta’’ tubers into popcorn-like tubers with cracked or fissures following the application of rimsulfuron. (a) Control; (b, c) 3 30 g ai/ha.
Table 5 Response of six potato cultivars to rimsulfuron applied at 20 g ai/ha in 2001a Potato cultivar
Application time (DAPE)
Phytotoxicity visual rating (%) (DAPE) 40b
60
90
Plant no. per row
Plant ht. (cm)
Columbus
Control 20 20/40 20/40/60
9a 8a 9a 8a
7ab 9a 8a 7ab
5bc 5bc 6ab 6ab
10a 11a 11a 10a
50f 50f 48f 49f
Farmer
Control 20 20/40 20/40/60
8a 9a 8a 8a
8a 8a 8a 9a
7a 8a 8a 8a
10a 10a 10a 10a
59a–c 54c–f 56c–e 54c–f
Recolta
Control 20 20/40 20/40/60
8a 8a 8a 8a
8a 8a 8a 8a
6ab 7a 7a 7a
9a 10a 10a 9a
63a 60a–c 63a 60a–c
Score
Control 20 20/40 20/40/60
8a 8a 8a 8a
7ab 8a 8a 8a
6ab 7a 7a 7a
9a 9a 9a 10a
64a 62ab 60a–c 64a
Timate
Control 20 20/40 20/40/60
8a 8a 8a 8a
7ab 9a 8a 7ab
5bc 8a 8a 8a
9a 9a 9a 9a
60a–c 60a–c 61a–c 55c–e
Spunta
Control 20 20/40 20/40/60
8a 8a 9a 9a
7ab 8a 9a 9a
5bc 5bc 5bc 5bc
10a 10a 10a 9a
57a–d 57c–f 56c–e 56c–e
a
Means followed by the same letter, within each column, do not significantly differ at the 5% level according to the LSD test. Scale (0 to 10), with 0 indicating complete death and 10 no injury.
b
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Table 6 Yield response of six potato cultivars to rimsulfuron applied at 20gai/ha in 2001a Potato cultivar
Application time (DAPE)
Total yield (kg/3.5 m2)
Tuber number (no./3.5 m2) Marketable
Non-marketable
Columbus
Control 20 20/40 20/40/60
12.2ab 12.0ab 10.0ab 14.4a
2.0e 4.0e 1.5e 6.0e
104b 93bc 110ab 128a
Farmer
Control 20 20/40 20/40/60
8.6bc 6.0cd 6.6cd 5.3de
0.5e 0.1e 0.5e 1.0e
72c–e 50e–g 80cd 61d–g
Recolta
Control 20 20/40 20/40/60
6.4cd 5.3de 6.6cd 6.0cd
4.0e 0.5e 1.5e 3.2e
53e–i 65d–f 71de 51e–i
Score
Control 20 20/40 20/40/60
8.0bc 12.0ab 10.2ab 12.2ab
21.0b 25.0ab 27.0ab 30.5a
31ij 67d–f 47f–j 51e–i
Timate
Control 20 20/40 20/40/60
6.4cd 14.0a 12.0ab 8.0bc
2.0e 18.0bc 12.0cd 6.6de
56e–h 61d–g 81cd 48f–i
Spunta
Control 20 20/40 20/40/60
4.0ef 2.2f 4.0ef 5.1de
0.5e 0.1e 0.1e 1.0e
34h–j 24j 39g–j 58d–g
a
Means followed by the same letter, within each column, do not significantly differ at the 5% level according to the LSD test.
as the yield obtained when applying rimsulfuron once but not twice. Although single or repeated application of rimsulfuron slightly increased the total yield of Columbus and Spunta, marketable yields and quality were severely damaged. The toxic effect of rimsulfuron on potato yield could be due to the sensitivity of potato cultivars, the use of surfactant and environmental factors in this region. Cultivar response to rimsulfuron ranged from very sensitive (Spunta, and Recolta), and moderately sensitive (Columbus and Farmer), to slightly sensitive (Timate and Score). These categories were based on total marketable yield and tuber injury caused by rimsulfuron application. Although no significant phytotoxic visual injury was caused by rimsulfuron in all cultivars, it reduced the marketable yield of Columbus, Farmer, Recolta and Spunta. Yield reduction reported here is more substantial than reported by others, especially since the maximum dose of rimsulfuron in our studies was 50 g ai/ha in 2000 and 20 g ai/ha in 2001, while various US potato cultivars are tolerant to 70 g/ha rimsulfuron without loss in yield or tuber quality (Eberlein et al., 1994). POST rimsulfuron applications require a nonionic surfactant for effective weed control (Green and Green, 1993). In our case, we suggest that rimsulfuron injury
may have resulted from the use of the surfactant which was used to enhance Orobanche control. Rimsulfuron at 20 g ai/ha without X-77 had no significant effect on Orobanche infestation (data not shown). Addition of X-77 to rimsulfuron may have increased rimsulfuron uptake resulting in better Orobanche control, but damaged the crop. It is important to note that crop injury symptoms were more severe in 2001 than in 2000. Higher temperature and lower rainfall were most likely responsible for low yield and crop injury in 2001. Further studies are needed to verify this.
Acknowledgments This research was supported by a grant from the University Research Board, American University of Beirut and from the Lebanese National Council for Scientific Research, Lebanon.
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ARTICLE IN PRESS M.A. Haidar et al. / Crop Protection 24 (2005) 7–13 Ackley, J.A., Wilson, H.P., Hines, T.E., 1997. Rimsulfuron and metribuzin efficacy in transplanted tomato (Lycopersicon esculentum). Weed Technol. 11, 324–328. Blackshaw, R.E., Lunch, D.R., Entz, T., 1995. Postemergence broadleaf weed control in potato (Solanum tuberosum) with rimsulfuron and HOE-075032. Weed Technol. 9, 228–235. Eberlein, C.V., Whitmore, J.C., Stanger, C.E., Guttieri, M.J., 1994. Postemergence weed control in potatoes (Solanum tuberosum) with rimsulfuron. Weed Technol. 8, 428–435. Goldwasser, Y., Eizenberg, H., Hershenhorn, J., Plakhine, D., Blumenfeld, T., Buxbaum, H., Golan, S., Kleifeld, Y., 2001. Control of Orobanche aegyptiaca and O. ramosa in potato. Crop Prot. 20, 403–410. Green, J.M., Green, J.H., 1993. Surfactant structure and concentration strongly affect rimsulfuron activity. Weed Technol. 7, 633–640. Haidar, M.A., Bibi, W., 1995. Common weeds of Lebanon, Arab and Near East Plant Protection Newsletter. Arab Society for Plant Protection, Beirut, Lebanon (abstract 34). Haidar, M.A., Sidahmed, M.M., 2000. Orobanche ramosa control with rimsulfuron in potato. Proceedings of the III International Weed Science Society. Foz Do Iguassu, Brazil (abstract 542). Haidar, M.A., Bibi, W., Sidahmad, M.M., 2003. Response of branched broomrape (Orobanche ramosa) growth and development to various soil amendments in potato. Crop Prot. 22, 291–294. Hershenhorn, J., Plakhine, D., Goldwasser, Y., Westwood, J.H., Foy, C.L., Kleifeld, Y., 1998. Effect of sulfonylurea herbicides
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on early development of Egyptian broomrape (Orobanche aegyptiaca) in tomato (Lycopersicon esculentum). Weed Technol. 12, 108–114. Kleifeld, Y., Goldwasser, Y., Herzlinger, G., Golan, S., Blumenfeld, T., Buxbaum, H., 1994. Selective control of broomrape in tomatoes with rimsulfuron. In: Pieterse, A.H., Verkleij, J.A.C., ter Borg, S.J. (Eds.), Proceedings of the Third Workshop on Orobanche and related Striga Research. Royal Tropical Institute, Amsterdam, pp. 561–571. Mekki, M., Leroux, G.D., 1994. Activity of nicosulfuron, rimsulfuron, and their mixture on field corn (Zea mays), soybean (Glycine max), and seven weed species. Weed Technol. 8, 436–440. Mitich, L.W., 1993. Orobanche—the broomrapes. Weed Technol. 7, 532–535. Mullen, R.J., Caprile, J., Viss, T.C., Rego, M., Brunmeier, D., Cancilla, C., Rivara, C.J., 2001. New weed management research in processing tomatoes. Acta Hortic. 542, 39–45. O’sullivan, J., Thomas, R.J., Bouw, W.J., 1998. Tolerance of sweet corn (Zea mays) cultivars to rimsulfuron. Weed Technol. 12, 258–261. Parker, C., Riches, C.R., 1993. Parasitic Weeds of the World: Biology and Control. Cab International, Wallingford, UK 332pp. Robinson, D.K., Monks, D.W., Monaco, T.J., 1996. Potato (Solanum tuberosum) tolerance and susceptibility of eight weeds to rimsulfuron with without metribuzin. Weed Technol. 10, 29–34.
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Susceptibility of Orobanche ramosa and potato tolerance to rimsulfuron M.A. Haidar, N. Iskandarani, M.M. Sidahmed, R. Darwish American University of Beirut, Faculty of Agricultural and Food Sciences, Riad-El-Solh, Beirut 1107 2020, Lebanon Received 11 May 2004; received in revised form 26 May 2004; accepted 1 June 2004
Abstract Field studies were conducted in Lebanon to examine Orobanche ramosa control, and the tolerance of six potato cultivars, to single or repeated foliar application of rimsulfuron. The effect of rimsulfuron was evaluated on a potato cultivar ‘‘Spunta’’ in 2000 and 2001, and on five new potato cultivars ‘‘Columbus’’, ‘‘Farmer’’, ‘‘Recolta’’, ‘‘Score’’ and ‘‘Timate’’ in 2001. The results indicate that both single and sequential applications of rimsulfuron between 20 and 50 g ai/ha significantly reduced Orobanche shoot number and dry weight compared to the control. Repeated applications (three times) was the most effective in reducing Orobanche shoot dry weight in all tested cultivars in comparison to their respective controls. Total potato yield within a cultivar was not reduced by single or sequential application of rimsulfuron, but marketable yield and tuber quality were significantly reduced in all cultivars (except for Score and Timate). Most tubers were small, fissured, and had a high incidence of malformed popcorn-like tubers. The most susceptible cultivars to Orobanche and sensitive to rimsulfuron were Spunta, followed by Recolta, Columbus, Farmer, Score and then Timate. Single or sequential application of rimsulfuron at 20 g ai/ha could be used to control Orobanche in Timate and Score cultivars. Although both varieties were slightly susceptible to repeated application of rimsulfuron, total and marketable yield was not affected. Additional research is required under different locations in Lebanon before a recommendation to growers for the use of rimsulfuron can be made. r 2004 Elsevier Ltd. All rights reserved. Keywords: Application timings; Lebanon; Cultivars
1. Introduction Orobanche ramosa Forsk (Branched broomrape) is a root-parasitic flowering plant in the family Orobanchaceae (Mitich, 1993). It parasitizes roots of a variety of herbaceous dicots, where it develops a physiological connection with the host xylem and phloem. O. ramosa is endemic in the Middle East and constitutes one of the most severe constraints to potato production in the region (Goldwasser et al., 2001; Haidar et al., 2003; Parker and Riches, 1993). Corresponding author. Department of Plant Sciences, American University of Beirut, FAFS, Riad El-Solh, Beirut 1107 2020, Lebanon. Tel.: +961-1-350000; fax: +961-1-74460. E-mail address: [email protected] (M.A. Haidar).
0261-2194/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.cropro.2004.06.007
Potato is one of the most important and widely grown crops in the Mediterranean region. Approximately 100,000 ha of potatoes are grown annually in Lebanon. Spunta is the most widely grown potato cultivar in Lebanon, but is highly susceptible to and damaged by O. ramosa (Haidar and Bibi, 1995). It is estimated that over 90% of the irrigated potato Spunta fields are parasitized by O. ramosa causing severe yield quantity and quality losses (Haidar, personal communication). Farmers are concerned about losses caused by this parasite and are seeking ways to control it. Currently, there are neither pre-emergence nor post-emergence (POST) herbicides, which control Orobanche in potato. Farmers rely on hand pulling and soil sterilization with highly volatile compounds for controlling Orobanche. These methods are expensive, injurious to the crop and
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cannot be applied economically on a large scale. Therefore, the search for new methods for controlling Orobanche has become increasingly important. Rimsulfuron is a POST sulfonylurea herbicide used for controlling many grasses and broadleaved weeds in field corn (Mekki and Leroux, 1994; O’sullivan et al., 1998), potato (Ackley et al., 1996; Blackshaw et al., 1995; Eberlein et al., 1994; Robinson et al., 1996) and tomato (Ackley et al., 1997; Mullen et al., 2001). Sequential application of rimsulfuron was also found effective in controlling O. aegyptiaca or O. ramosa in tomato (Hershenhorn et al., 1998; Kleifeld et al., 1994) and potato (Goldwasser et al., 2001; Haidar and Sidahmed, 2000). However, little is known about its efficacy and selectivity under Lebanese irrigated field conditions, although deformed potato tubers of the standard potato cultivar ‘‘Spunta’’ were observed following rimsulfuron application (Haidar and Sidahmed, 2000). Thus, more information is required about its efficacy against Orobanche and selectivity of potato cultivars to rimsulfuron. Studies were initiated to determine (a) rimsulfuron doses and time of application required to control O. ramosa, and (b) the response of six potato cultivars to rimsulfuron.
2. Materials and methods 2.1. General experimental procedures Experiments were conducted in a field naturally infested with O. ramosa at the Agricultural Research and Education Center (AREC) of the American University of Beirut, Lebanon in 2000 and 2001. The AREC is located in the Northern Central Beqa’a plain of Lebanon. The soil was silty clay loam with a pH of 7.41, EC 0.24 ms/cm and 2.4% organic matter. In both years, all plots were tilled twice with a mouldboard, disked and levelled 2 weeks prior to planting. The experimental area received a uniform application of 2.5 t/ha of NPK (17:17:17) before disking each year. Nitrogen was applied 40 days after planting at a rate of 300 kg/ha each year. Plots were sprinkler irrigated every 8 days. The standard potato cultivar Spunta was planted on April 25, 2000, while five new potato cultivars Columbus, Farmer, Recolta, Score and Timate (Nederlandse Algemene Keuringsdienst-NAK) were planted on April 13, 2001. In both years, tuber pieces of potato cultivars were planted at 3.0 t/ha in the same field but at different spots. Plots (5 m long and 2.2 m wide) were hilled 6 weeks after planting (standard practice by Lebanese farmers). Potato rows were 0.7 m apart and within-therow spacing was around 0.35 m. To eliminate all weeds other than Orobanche, the entire experimental area received a standard application of metribuzin (SencorR,
70%) at 0.65 kg ai/ha 1 week after sowing each year. It is worth mentioning that metribuzin is widely used by Lebanese potato growers and is known to be safe when applied to potato. Rimsulfuron (Technical grade, 75% DF, from Dupont) was applied POST with a CO2-pressurized backpack sprayer that delivered 310 l/ha at 138 kPa through a Teejet 8002 flat fan spray tips. In 2000, rimsulfuron was applied at 10, 20, 30, 40 and 50 g ai/ha, while in 2001 rimsulfuron was applied at a single dose of 20 g ai/ha. Each dose was tested for single and repeated (twice or three times) application at 20, 40 and 60 days after potato emergence (DAPE). Plots were irrigated 2 days after each spraying. Potato plants were 8–12 cm tall at 20 DAPE. Nonionic surfactant (X-77) at 0.2%(v/v) was added to the spray solution. 2.2. Experimental measurements and statistical analyses Experimental plots (3 rows/plot) were arranged in a factorial randomized complete block design with five replications. Factors evaluated were rimsulfuron doses, application timing (20, 40 and 60 DAPE) and potato cultivars. Statistical analysis was done separately for the 2000 and 2001 data. All data were subjected to analysis of variance and Fisher’s protected least significant difference (LSD) test at p ¼ 0:05 level of probability was used to determine significant differences between treatment means. Orobanche data included Orobanche shoot number (75 and 90 DAPE) and shoot dry weight per 2 m2. Potato data included phytotoxicity visual rating (40, 60 and 90 DAPE), number of shoots of the middle row (40 DAPE), height (90 DAPE, 5 plants/ plot), total yield and tuber number of marketable and non-marketable yield. Potato yield was determined by harvesting the middle row (3.5 m2) in each plot. Yield quality was determined by separating harvested tubers into two classes: marketable (45:0 cm in diameter) and non-marketable tubers (o5:0 cm in diameter) according to Robinson et al. (1996).
3. Results and discussion 3.1. Orobanche management in 2000 Single or repeated application of rimsulfuron at all tested doses delayed the appearance and emergence of Orobanche shoots 75 DAPE as compared to the control (Table 1). Except for a single application of rimsulfuron at 10 g ai/ha, all tested doses significantly reduced Orobanche shoot number in Spunta 90 DAPE and shoot dry weight compared to the control. Rimsulfuron at 20 g ai/ha reduced Orobanche infestation by 94% when applied twice (20 and 40 DAPE) and 98.5% when applied three times (20, 40 and 60 DAPE). The greatest
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Table 1 Effect of rimsulfuron on average Orobanche shoot count and weight per 2 m2 in 2000a
Table 2 Effect of rimsulfuron (20 g ai/ha) on average Orobanche shoot count and dry weight per 2 m2 in 2001a
Rimsulfuron dose (g ai/ha)
Potato cultivar
Application time (DAPE)
10 20 30 40 50
20 20 20 20 20
10 20 30 40 50
20/40 20/40 20/40 20/40 20/40
10 20 30 40 50 Control
20/40/60 20/40/60 20/40/60 20/40/60 20/40/60 —
Shoot number
Shoot dry wt. (g)
75
90
53b 1c 0c 13c 0c
119ab 56b–d 29cd 84bc 36cd
61a 36b 15bc 20bc 17bc
0c 0c 0c 0c 0c
32cd 12cd 3d 0d 3d
12c 5c 1c 0c 1c
0c 0c 0 0c 0c 96a
5.7d 2.9d 0d 0d 0d 194a
3c 1c 0c 0c 0c 740a
reduction in shoot number and dry weight were recorded with repeated application (two or three times) of rimsulfuron at all tested doses (Table 1). Three sequential applications of rimsulfuron at 12.5 or 25 g/ha significantly reduced O. aegyptiaca infestation in potato (Goldwasser et al., 2001).
Shoot number (DAPE) 75
90
Shoot dry wt. (g)
Columbus
Control 20 20/40 20/40/60
213c 56ef 34ef 12f
174d 78fg 38g 38g
193d 91f–h 73gh 57gh
Farmer
Control 20 20/40 20/40/60
174cd 33ef 16f 22ef
297b 123de 115ef 36g
214d 154d–f 163de 64gh
Recolta
Control 20 20/40 20/40/60
324b 99de 39ef 52ef
285c 193d 98ef 70fg
271cd 207d 198d 112e–g
Score
Control 20 20/40 20/40/60
207c 46ef 25ef 32ef
286c 82fg 44g 36g
200d 85fg 40h 47h
Timate
Control 20 20/40 20/40/60
154cd 18f 22ef 15f
176d 66fg 80fg 29g
163de 91f–h 65gh 24h
Spunta
Control 20 20/40 20/40/60
440a 102de 45ef 52ef
400a 280c 142de 96ef
423a 328bc 323bc 271cd
a
Means followed by the same letter, within each column, do not significantly differ at the 5% level according to the LSD test.
Application time (DAPE)
a
Means followed by the same letter, within each column, do not significantly differ at the 5% level according to the LSD test.
3.2. Orobanche management in 2001 Single or repeated application of rimsulfuron at 20 g ai/ha significantly reduced Orobanche shoot number after 75 and 90 DAPE in all potato cultivars in comparison to their respective controls (Table 2). Repeated application of rimsulfuron (three times) was the most effective treatment in reducing Orobanche shoot dry weight in all tested cultivars in comparison to their respective controls. Our results suggest that Spunta is the most susceptible potato cultivar to O. ramosa. The highest Orobanche shoot count recorded was in the control treatment of Spunta in comparison to the controls of all cultivars. Cultivar susceptibility to O. ramosa ranged from very sensitive (Spunta, and Recolta), to sensitive (Timate and Score), with Columbus and Farmer cultivars showing moderate sensitivity. 3.3. Potato biomass and yield in 2000 Single or repeated application of rimsulfuron at 30 g ai/ha or above was toxic to Spunta early in the season (after 40 DAPE). Visual potato injury appeared 8 days after first spraying and included small leaves, purple venation of leaves, plant stunting and compact potato
plants, compared to the control (Table 3). Potato injury was similar to that in other studies (Blackshaw et al., 1995; Eberlein et al., 1994). No crop injury was observed later in the season (after 60 and 90 DAPE). Eberlein et al. (1994) observed visual injury on potato plants 1 week after spraying rimsulfuron at 15–70 g/ha, but disappeared later in the season. Rimsulfuron at all doses had no significant effect on potato plant number. However, single or repeated applications at 20 g ai/ha and above significantly reduced potato shoot height. The highest reduction in potato height was observed with repeated application of rimsulfuron at 40–50 g ai/ha (Table 3). All doses of rimsulfuron slowed down potato growth and delayed crop maturity. Our observations were similar to those of Mullen et al. (2001), that rimsulfuron delayed the maturity of tomato plants. Single or repeated application of rimsulfuron between 10 and 30 g ai/ha significantly increased total yield of Spunta, but reduced marketable yield (Table 4). All doses of rimsulfuron produced non-marketable potato tubers. Phytotoxicity was mostly reflected in the tuber quality of potato yield grown for fresh market with a high incidence of deformed and small tubers (Fig. 1).
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Table 3 Response of potato cultivar ‘‘Spunta’’ to rimsulfuron in 2000a Rimsulfuron dose (g ai/ha)
Application time (DAPE)
Phytotoxicity visual rating (%) (DAPE) b
40
60
90
Plant no.per row
Plant ht. (cm)
10 20 30 40 50
20 20 20 20 20
8a 8a 6ab 6ab 6ab
9a 8a 9a 8a 9a
9a 8a 9a 8a 9a
16a 16a 17a 16a 17a
49.5ab 44.5b–d 49.5ab 45.8b–d 44.3b–d
10 20 30 40 50
20/40 20/40 20/40 20/40 20/40
8a 8a 6ab 6ab 6ab
9a 8a 7ab 7ab 7ab
9a 8a 8a 8a 6ab
16a 17a 17a 18a 16a
49.3a–c 45.8b–d 41.8b–d 38.5d 40.3cd
10 20 30 40 50 Control
20/40/60 20/40/60 20/40/60 20/40/60 20/40/60 —
8a 8a 8a 6ab 6ab 9a
8a 8a 8a 8a 8a 9a
8a 8a 8a 8a 8a 9a
17a 17a 18a 16a 16a 16a
48.3ab 45.5b–d 42.3b–d 39.8d 41.3b–d 56.3a
a
Means followed by the same letter, within each column, do not significantly differ at the 5% level according to the LSD test. Scale (0–10), with 0 indicating complete death and 10 no injury.
b
Table 4 Yield response of potato cultivar ‘‘Spunta’’ to rimsulfuron in 2000a Rimsulfuron dose (g ai/ha)
Application time (DAPE)
Total yield (kg/3.5 m2)
Tuber number (no./3.5 m2) Marketable
Non-marketable
10 20 30 40 50
20 20 20 20 20
10.6b 9.5b 9.9b 7.4a 7.2a
0.2a 0.3a 0.3a 0.5a 0.1a
101ab 103ab 120a 72bc 81ab
10 20 30 40 50
20/40 20/40 20/40 20/40 20/40
10.9bc 11.1bc 8.5b 7.1a 7.4a
0.2a 0.0a 0.2a 0.0a 0.1a
52bc 79bc 66bc 48c 53bc
10 20 30 40 50 Control
20/40/60 20/40/60 20/40/60 20/40/60 20/40/60 —
10.4b 9.0b 8.5b 5.9a 7.1a 7.2a
0.1a 0.2a 0.2a 0.0a 0.0a 0.4a
130a 110a 45c 53bc 71bc 51bc
a
Means followed by the same letter, within each column, do not significantly differ at the 5% level according to the LSD test.
Although potato tubers were small and deformed, the significance difference in total yield compared to the control (Table 4) was due to the increase in the number of non-marketable tubers. The rate of deformed tubers increased with rimsulfuron dose and application time. Although repeated application of rimsulfuron was very effective in reducing Orobanche infestation, potato yield was severely damaged. Previous studies by Goldwasser
et al. (2001) and Eberlein et al. (1994) indicated that rimsulfuron at 15–70 g/ha was not toxic to potato, but our results suggest that repeated application of rimsulfuron at 10–50 g ai/ha significantly reduced marketable potato yield and tuber quality. Potato producers should be aware that repeated application of rimsulfuron at 10–50 g ai/ha can delay crop maturity and reduce crop quality of the cultivar Spunta.
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3.4. Potato biomass and yield in 2001
(b)
(a)
11
Results in Table 5 indicate that single or repeated application of rimsulfuron were not phytotoxic to all cultivars with respect to crop vigor, stand and number of plants in comparison to their respective controls. Also, plant height within a cultivar was not significantly affected by single or repeated application of rimsulfuron. Significant differences were found in potato yield between different treatments and cultivars. The lowest yield obtained was in Spunta, which was significantly lower than the other cultivars (Table 6). The highest total yielding cultivar was Columbus, with the repeated application of rimsulfuron (three times) yielding the highest, although it is not significantly different from other treatments. The second highest yielding cultivars were Timate or Score, where the highest yield was obtained with single or repeated application of rimsulfuron. Columbus, Farmer, Recolta and Score showed no significant differences between the different treatments. Applying Rimsulfuron once or twice significantly increased the total potato yield of Timate in comparison to the control. Applying rimsulfuron three times to Spunta gave the highest non-marketable potato yield, which was significantly different from the control as well
(c)
Fig. 1. Deformed potato ‘‘Spunta’’ tubers into popcorn-like tubers with cracked or fissures following the application of rimsulfuron. (a) Control; (b, c) 3 30 g ai/ha.
Table 5 Response of six potato cultivars to rimsulfuron applied at 20 g ai/ha in 2001a Potato cultivar
Application time (DAPE)
Phytotoxicity visual rating (%) (DAPE) 40b
60
90
Plant no. per row
Plant ht. (cm)
Columbus
Control 20 20/40 20/40/60
9a 8a 9a 8a
7ab 9a 8a 7ab
5bc 5bc 6ab 6ab
10a 11a 11a 10a
50f 50f 48f 49f
Farmer
Control 20 20/40 20/40/60
8a 9a 8a 8a
8a 8a 8a 9a
7a 8a 8a 8a
10a 10a 10a 10a
59a–c 54c–f 56c–e 54c–f
Recolta
Control 20 20/40 20/40/60
8a 8a 8a 8a
8a 8a 8a 8a
6ab 7a 7a 7a
9a 10a 10a 9a
63a 60a–c 63a 60a–c
Score
Control 20 20/40 20/40/60
8a 8a 8a 8a
7ab 8a 8a 8a
6ab 7a 7a 7a
9a 9a 9a 10a
64a 62ab 60a–c 64a
Timate
Control 20 20/40 20/40/60
8a 8a 8a 8a
7ab 9a 8a 7ab
5bc 8a 8a 8a
9a 9a 9a 9a
60a–c 60a–c 61a–c 55c–e
Spunta
Control 20 20/40 20/40/60
8a 8a 9a 9a
7ab 8a 9a 9a
5bc 5bc 5bc 5bc
10a 10a 10a 9a
57a–d 57c–f 56c–e 56c–e
a
Means followed by the same letter, within each column, do not significantly differ at the 5% level according to the LSD test. Scale (0 to 10), with 0 indicating complete death and 10 no injury.
b
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Table 6 Yield response of six potato cultivars to rimsulfuron applied at 20gai/ha in 2001a Potato cultivar
Application time (DAPE)
Total yield (kg/3.5 m2)
Tuber number (no./3.5 m2) Marketable
Non-marketable
Columbus
Control 20 20/40 20/40/60
12.2ab 12.0ab 10.0ab 14.4a
2.0e 4.0e 1.5e 6.0e
104b 93bc 110ab 128a
Farmer
Control 20 20/40 20/40/60
8.6bc 6.0cd 6.6cd 5.3de
0.5e 0.1e 0.5e 1.0e
72c–e 50e–g 80cd 61d–g
Recolta
Control 20 20/40 20/40/60
6.4cd 5.3de 6.6cd 6.0cd
4.0e 0.5e 1.5e 3.2e
53e–i 65d–f 71de 51e–i
Score
Control 20 20/40 20/40/60
8.0bc 12.0ab 10.2ab 12.2ab
21.0b 25.0ab 27.0ab 30.5a
31ij 67d–f 47f–j 51e–i
Timate
Control 20 20/40 20/40/60
6.4cd 14.0a 12.0ab 8.0bc
2.0e 18.0bc 12.0cd 6.6de
56e–h 61d–g 81cd 48f–i
Spunta
Control 20 20/40 20/40/60
4.0ef 2.2f 4.0ef 5.1de
0.5e 0.1e 0.1e 1.0e
34h–j 24j 39g–j 58d–g
a
Means followed by the same letter, within each column, do not significantly differ at the 5% level according to the LSD test.
as the yield obtained when applying rimsulfuron once but not twice. Although single or repeated application of rimsulfuron slightly increased the total yield of Columbus and Spunta, marketable yields and quality were severely damaged. The toxic effect of rimsulfuron on potato yield could be due to the sensitivity of potato cultivars, the use of surfactant and environmental factors in this region. Cultivar response to rimsulfuron ranged from very sensitive (Spunta, and Recolta), and moderately sensitive (Columbus and Farmer), to slightly sensitive (Timate and Score). These categories were based on total marketable yield and tuber injury caused by rimsulfuron application. Although no significant phytotoxic visual injury was caused by rimsulfuron in all cultivars, it reduced the marketable yield of Columbus, Farmer, Recolta and Spunta. Yield reduction reported here is more substantial than reported by others, especially since the maximum dose of rimsulfuron in our studies was 50 g ai/ha in 2000 and 20 g ai/ha in 2001, while various US potato cultivars are tolerant to 70 g/ha rimsulfuron without loss in yield or tuber quality (Eberlein et al., 1994). POST rimsulfuron applications require a nonionic surfactant for effective weed control (Green and Green, 1993). In our case, we suggest that rimsulfuron injury
may have resulted from the use of the surfactant which was used to enhance Orobanche control. Rimsulfuron at 20 g ai/ha without X-77 had no significant effect on Orobanche infestation (data not shown). Addition of X-77 to rimsulfuron may have increased rimsulfuron uptake resulting in better Orobanche control, but damaged the crop. It is important to note that crop injury symptoms were more severe in 2001 than in 2000. Higher temperature and lower rainfall were most likely responsible for low yield and crop injury in 2001. Further studies are needed to verify this.
Acknowledgments This research was supported by a grant from the University Research Board, American University of Beirut and from the Lebanese National Council for Scientific Research, Lebanon.
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