Management of Root and Bulb Rot Affecting Some Flower Bulb Production in Egypt

Results and Discussion

Isolation, identification and frequency of fungi associated with infected lilium with root and bulb rot

Two hundred and thirty-seven fungal isolates belonging to five genera and nine species were recovered from diseased lilium showing root and bulb rot symptoms collected from different fields located at Qaluobia Governorate. The isolated fungi were identified as Aspergillus niger Tiegh (3 isolates), Fusarium moniliforme J. Sheld (10 isolates), F. oxysporum Schltdl. (100 isolates), F. roseum Beck (20 isolates), F. semitectum Berk (11 isolates), F. solani (Mart.) Sacc. (16 isolates), Pythium spp. (Pringsh.) (45 isolates), Rhizoctonia solani Kühn (30 isolates) and Rhizopus arrizhus Fischer (2 isolates). Data in table (1) indicate that the most dominant fungi were F. oxysporum (42.14%), followed by Pythium spp. (18.99%), R. solani (12.66%) and F. roseum (8.44%). Meanwhile, Rh. arrizhus recorded less frequency (0.84%). These results are in agreement with those obtained by Hilal et al. (1992); Wright (1998) and Ciampi et al. (2009) who found that 20% of the isolated fungi from calla bulbs was Fusarium solani (Mart.) Sacc. and 80% was F. oxysporum Schltdl. On the other hand, Mordechai-Sara et al. (2014) reported that leaf chlorosis, wilt, root and bulb rot of lily plants grown in commercial greenhouses in Israel are predominantly caused by Rhizoctonia AG-A, Pythium oligandrum and Fusarium proliferatum. Also, Lakshman et al. (2017) stated that eight fungal isolates were recovered from necrotic roots of Easter lilies (Lilium longiflorum cv. Nellie White) and grown in a field located at the U.S. Pacific Northwest. The eight fungal isolates identified by sequencing and molecular phylogenetic analyses based on their ITS rDNA region. Five isolates were identified as Fusarium oxysporum, two as F. tricinctum, and one as Rhizoctonia sp. AG-I.

Solated fungi, i.e. oxysporum, F. roseum, R. solani and Pythium spp., infecting lilium was determined under greenhouse conditions. Fig. (1) shows that F. oxysporum (31.25 and 37.50%, 30 and 60 days after planting, respectively), followed by Pythium spp. (18.75 and 37.50%, 30 and 60 days after planting, respectively), was the most virulent ones. F. roseum (18.75 and 25.00%, 30 and 60 days after planting, respectively), followed by R. solani (12.50 and 25.00%, 30 and 60 days after planting, respectively), was the lowest ones. These results are in agreement with those obtained by Hilal et al. (1992), Schineider et al. (2001), Elewa et al. (2001), Chase (2005), Palmero et al. (2014) and Mordechai-Sara et al. (2014) who reported that artificially inoculated lily plants with each of R. solani AG-A, P. oligandrum, F. oxysporum and F. proliferatum resulted in chlorosis on low leaves 7 days after inoculation. Eight weeks later, symptoms became more severe and accompanied by wilting.

Host range

Two trials were carried out to test the capability of the tested fungi, i.e. F. oxysporum, F. roseum, R. solani and Pythium spp. to infect tulip, lilium, iris, calla and freesia either to bulbs in laboratory or greenhouse on developed plants:

Laboratory bulb tests

The ability of the tested fungi to infect bulbs of tulip, lilium, iris, calla and freesia was determined under laboratory conditions. Data in table (2) show that the tested fungi differed in their pathogenic potentialities to infect the bulbs of the tested plants. F. oxysporum was the most virulent one, resulted in 83.33, 91.66, 83.33, 25.00 and 83.33% disease severity to the tested plants, respectively. Pythium spp. followed by F. roseum occupied the second rank. R. solani was the lowest pathogenic fungus, giving 25, 25, 16.66, 8.33 and 25% disease severity, respectively. Moreover, lillium bulbs were the most susceptible to the tested pathogens, especially F. oxysporum, being 91.66% disease severity. Meanwhile, calla was the lowest susceptible one (Table 2). The high susceptibility of lilium bulbs to infection may be due to the characteristics of its bulbs, which have no dry scale structure (tunica) for protecting the bulbs from the external factors. Also, lillium bulbs have higher moisture content than other geophytes, and they have thicker and succulent scales, thus, it is easy for the pathogens to penetrate into cells through the scales (Sirin, 2011).

Greenhouse tests

Under greenhouse conditions, the capability of the tested fungi, i.e. F. oxysporum, F. roseum, R. solani and Pythium spp. to infect tulip, lilium, iris, calla and freesia was determined. Data in table (3) show that the four tested fungi differed in their pathogenic capabilities to infect the tested bulbs. F. oxysporum and Pythium spp. were the most aggressive fungi on all tested bulbs, since they gave the highest infection percentages. On the other hand, lilium and iris were the most susceptible ones, while calla bulbs were the less susceptible ones. These results are in agreement with those obtained by Wright (1998) and Ciampi et al. (2009). Elewa et al. (2001) reported that testing susceptibility of some bulbous ornamental plants to infection by F. oxysporum f. sp. gladioli revealed that freesia and iris were the most susceptible hosts (100% infection), while lilium and tulip were the lowest ones.

Alternative against a number of pathogens for effective and sustainable disease control management of several flower bulbs (Lu and Chen, 2005 and Luzzatto-Knaana and Yedidia, 2009). In this study the efficacy of two commercial bioformulations and two chemical inducers against lilium and calla root rot caused by F. oxysporum was estimated by counting the percentage of the infected plants 60 days after planting. Data in table (4) indicate that all the tested treatments significantly decreased the disease incidence and increased the survived plants in comparison to the untreated control. The decrease in disease percentages in relation to the untreated control ranged from (9.90 to 40.00%) in lilium plants and from (15.33 to 66.66%) in calla plants. The increase in the survived plants ranged from 16.50 to 66.66% and from 10.0 to 40.0%, in lilium and calla, respectively. Bio cure-B and followed by Bio cure-F were the best treatments at significant level, while Chito Care was the lowest effective one. These results are somewhat in agreement with those obtained by Elmer (2006) who reported that Benzo (1, 2, 3)-thiadiazole-7-carbothiolic acid (BTH) protected corms of gladiolus (Gladiolus hortulanus) from attack with F. oxysporum f. sp. gladioli. Also, Liu et al. (2008) reported that application of cell suspension of Bacillus cereus strain C1L as soil drench 24 h before inoculation with Botrytis elliptica reduced disease severity by (40%) in Lilium formosanum seedlings. Also, Sirin (2011) confirmed the potentiality of T. harzianum in controlling R. solani on lilium plants under in vivo conditions.

Integrated effect of some commercial bio-formulations and chemical inducers on lilium root rot under greenhouse conditions

This experiment was conducted to determine the integrated effect of the tested inducers and biocontrol formulations, Bio-Cure–F and Bio-Cure-B on lilium root rot control. Data in table (5) show that dipping bulbs of lilium in formula of the tested biocontrol agents and treated with any of the tested chemical inducers as soil drench immediately after planting significantly protected plants from Fusarium root rot. The integration between P. fluorescens and any of the tested inducers was more effective than integration between T. viride and the same inducers in relation to the disease incidence percentages. Potassium silicate in combination with P. fluorescens was the most effective treatment, which resulted in the lowest disease incidence percentage, being 31.25% (Table 5). These results are in harmony with those obtained by Mishar et al. (2000); Abdel-Monaim (2008); Kidane, (2008); El-Mohamedy et al. (2014) and Khalifa et al. (2016). Elmer (2006) evaluated the efficacy of pre plant treatments of gladiolus corms with combinations of acibenzolar -S - methyl (ASM) and biological or chemical fungicides for suppression of Fusarium corm rot. He found that corms treated with ASM produced 48% more marketable flower spikes than untreated corms and the value of the area under the disease progress curve (AUDPC) was reduced by 12%.

However, chemical fungicides Medallion Reg 50WP (fludiozonil) and Terranguard TM 50WP (triflumizole) reduced AUDPC by 27% and 23%, respectively, and none of the biological fungicides were effective. Improved plant resistance to diseases by silicon (Si) applications has been reported for different crops. Because of pathogenic fungi penetrate the host through the epidermal cell wall; Si deposited in these walls may act as a mechanical barrier. Recently, research prove that the production and accumulation of antifungal phenolic compounds such as lignin and activation of defence related enzymes, including chitinase and 1,3-glucanase may also be involved (Smith-Linda et al., 2005). On the other hand, fungi causing symptoms of Fusarium wilt can survive in the soil in a dormant state for many years by forming resistant spores called chlamydospores. Like many other pathogenic soil borne fungi, in order to infect plant roots, their dormant units must be stimulated by molecules present in seed and root exudates. Without the release of such stimulatory molecules, in most cases, root infections hardly take place (Kidane, 2008). Also, silicon may reduce or delay spore germination and fungal growth indirectly by reducing amino acid and starch formation, which promote fungal growth (Takahashi, 1995 and Kidane, 2008).