# Inheritance of resistance to alfalfa mosaic virus in Lycopersicon hirsutum f. glabratum PI 134417

Giuseppe Parrella, H. Laterrot, Kahsay Gebre Selassie, Georges Marchoux

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Giuseppe Parrella, H. Laterrot, Kahsay Gebre Selassie, Georges Marchoux. Inheritance of resistance to alfalfa mosaic virus in Lycopersicon hirsutum f. glabratum PI 134417. Journal of Plant Pathology, 1998, 80 (3), pp.241-243. 10.4454/jpp.v80i3.824. hal-02694959

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SHORT COMMUNICATION

INHERITANCE OF RESISTANCE TO ALFALFA MOSAIC VIRUS
IN *LYCOPERSICON HIRSUTUM* f. *GLABRATUM* PI 134417

G. Parrella<fnref n="1" />, H. Laterrot<fnref n="2" />, K. Gebre Selassie<fnref n="3" />, G. Marchoux<fnref n="3" />

SUMMARY

Alfalfa mosaic virus (AMV) is of sporadic occur-
rence in tomato crops. More recently, important epi-
demics caused by AMV have been reported in field-
grown canning tomatoes in southern Italy. Since no
lines or commercial varieties resistant to AMV are avail-
able, we have studied the inheritance of resistance to
this virus, derived from the accession of *Lycopersicon
hirsutum* f. *glabratum* PI 134417. A necrogenic tomato
isolate of AMV was used as source of inoculum. Visual
observations of symptoms and enzyme-linked im-
munosorbent assay (ELISA) were used to screen plants
after mechanical inoculation. All the F₁ tested were re-
sistant while the segregation ratios of F₂ and BC₁ gener-
ations were consistent with a simple dominant inheri-
tance. We propose tentatively to name this gene *Am*.

RIASSUNTO

EREDITÀ DELLA RESISTENZA AL VIRUS DEL MOSAICO
DELL'ERBA MEDICA NELL'ACCESSIONE PI 134417 DI LY-
COPERSICON HIRSUTUM F. GLABRATUM. Negli ultimi
anni sono state segnalate numerose epidemie causate
dal virus del mosaico dell'erba medica (AMV) in coltu-
re di pomodoro da industria nel sud dell'Italia. Attual-
mente non è disponibile nessuna linea o varietà com-
merciale di pomodoro resistente a tale virus. Il presente
lavoro riporta i risultati relativi allo studio dell'eredità
della resistenza a tale virus derivata dall'accessione di
*Lycopersicon hirsutum* f. *glabratum* PI 134417. A tale
scopo è stato utilizzato come fonte di inoculo un isolato
di AMV necrogenico su pomodoro. Le piante inoculate
meccanicamente sono state valutate per la resistenza
mediante saggi ELISA ed osservazioni dei sintomi. Tut-
te le piante F₁ sono risultate resistenti mentre i rapporti
di segregazione ottenuti nelle generazioni F₂ e BC₁ era-
no in accordo con un eredità monogenica dominante.
Per tale gene è stato proposto il simbolo *Am*.

Key words: Lycopersicon hirsutum, inheritance, alfal-
fa mosaic virus.

Alfalfa mosaic virus (AMV; *Bromoviridae*) is a plant pathogen with worldwide distribution, transmitted non-persistently by at least 22 aphid species and by seed in some alfalfa varieties and solanaceous species (Edwardson and Christie, 1986). It can infect most solanaceous crops in the field, causing severe losses to pepper (Berkeley, 1947; Kovacevski, 1965; Hamm *et al.*, 1995), tobacco (Conti and Vegetti, 1970; Vuittenez *et al.*, 1974; Tedford and Nielsen, 1990), potato (Black and Prince, 1940) and is of lesser economic importance to eggplant (Crill *et al.*, 1970; Marchoux and Rougier, 1974; Kemp and Troup, 1977).

AMV infections in tomato are generally sporadic, but
in the last few years epiphytotics of a necrotic phenotype
have occurred in southern Italy and southern France
(Ragozzino, 1995; Finetti Sialer et al., 1997; Parrella et
al., 1997). Historically, most AMV infections in tomato
were associated with the presence of alfalfa crops nearby
(Zitter, 1993). However, this was not the case with the
latest reports from Italy and France, where natural reser-
voirs of the virus were not identified.

As with other non-persistently transmitted viruses
with a wide host range, control of AMV is difficult.
Spraying to reduce aphid populations does not prevent
primary infection and usually requires heavy pesticide
use. Physical barriers, such as nets, are useful in nur-
series or in greenhouse crops, but are unmanageable in
the open field. The best way to reduce losses would be
to use resistant or tolerant tomato varieties, but to our
knowledge, no such varieties are commercially avail-
able. However, we have recently reported three poten-
tial sources of AMV resistance in *Lycopersicon hirsutum*
accessions (Parrella *et al.*, 1997). In the present study,
we have determined the inheritance of resistance in one
of these resistant *L. hirsutum* accessions to be used in
tomato breeding programmes.

*L. hirsutum* f. *glabratum* PI 134417 was used as
donor of resistance to AMV, while the genotypes Mo-

<footnote n="1">¹Centro di Studio del CNR sui Virus e le Virosi delle Colture Mediterranee, Via G. Amendola 165/a, I-70126 Bari, Italy</footnote>

<footnote n="2">²INRA, Station d'Amelioration des Plantes Maraîchères, BP 94, F84143 Montfavet Cedex, France</footnote>

<footnote n="3">³INRA, Station de Pathologie Végétale, BP 94, F84143, Montfavet Cedex, France</footnote>
mor of *L. esculentum* and PI 247087 Australia of *L. hirsutum* f. *glabratum* were used as susceptible controls (Parrella *et al.*, 1997) and were crossed with PI 134417.

For the inheritance study, the following generations were used: $F_1$ (Momor x PI 134417), $F_1$ (PI 134417 x PI 247087), $F_1$ (PI 247087 x PI 134417), $F_2$ progenies (Momor x PI 134417) and (PI 134417 x PI 247087) obtained by $F_1$ intercrossing, and the first generation of backcross $BC_1$ PI 247087 x (PI 134417 x PI 247087).

Seedlings were transplanted at the cotyledon stage to 10 cm diameter pots with peat bog-moss as substrate and watered weekly with a nutrient solution. All plants were grown in an insect-proof greenhouse (22-26°C and 70-80% humidity) under natural lighting.

The AMV isolate LYH-1 (Parrella *et al.*, 1997) was used as source of inoculum, and was maintained and multiplied in *Nicotiana tabacum* cv. 'Xanthi' n.c. Inoculum was prepared by grinding 1 g of young tobacco leaves in 4 ml of 0.03 M $Na_2HPO_4$ buffer containing 0.2% sodium diethyldithiocarbamate. Before inoculation, 75 mg ml$^{-1}$ of carborundum and activated charcoal were added to the sap extract (Marrou, 1967). The slurry was used to inoculate cotyledons and the first two true leaves of 16-day-old seedlings.

Symptoms were observed from one day up to one month after inoculation. Samples from uninoculated leaves were tested 15 and 30 days after inoculation by using DAS-ELISA as described by Clark and Adams

(1977). Plant extracts were prepared by grinding 1 g of leaves in 4 ml of inoculation buffer with a leaf press.

An antiserum (kindly supplied by H. Lot, INRA, Avignon) to an isolate of AMV from lettuce was used. Plates were read with a Tirtertek Multiskan Plus Photometer at 405 nm 1 h after addition of the substrate. Samples were considered positive when the absorbance value was more than twice the mean of the healthy controls.

*L. hirsutum* f. *glabratum* PI 134417 showed no reaction to infection and no symptoms for at least 1 month after inoculation both in inoculated and uninoculated leaves, and no virus was detected by ELISA 15 and 30 days after inoculation in the same tissues (Table 1). The susceptible controls, Momor and the *hirsutum* accession PI 247087 Australia, reacted with prominent local and systemic necrosis few days after inoculation, followed by death of the plant.

Plants of the three $F_1$ Momor x PI 134417, PI 134417 x PI 247087 and PI 247087 x PI 134417, behaved like the resistant parent and showed no symptoms in inoculated and uninoculated leaves, which were also negative when checked by ELISA 15 and 30 days after inoculation. The resistance was therefore dominant regardless of the resistant parent.

$F_2$ plants deriving from the crosses Momor x PI 134417 and PI 134417 x PI 247087 segregated in the ratio 3 resistant to 1 susceptible. Further confirmation of the presence of a single dominant gene was obtained

<table><caption>**Table 1.** Reaction of parents Momor (susceptible), PI 134417 (resistant), PI 247087 (susceptible) and segregating generations to inoculation with AMV isolate LYH-1, based on symptoms development and ELISA results.</caption><thead><tr><th rowspan="2">Genotypes</th><th rowspan="2">no. plants</th><th colspan="4">Symptoms</th><th colspan="4">ELISA</th></tr><tr><th>S/R</th><th>expected ratio</th><th>χ<sup>2</sup></th><th>P</th><th>+/-</th><th>expected ratio</th><th>χ<sup>2</sup></th><th>P</th></tr></thead><tbody><tr><td>Momor (P1)</td><td>30</td><td>30<sup>a</sup>/0</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>PI 134417 (P2)</td><td>30</td><td>0/30</td><td></td><td></td><td></td><td>0/30</td><td></td><td></td><td></td></tr><tr><td>PI 247087 (P3)</td><td>30</td><td>30<sup>a</sup>/0</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>F<sub>1</sub> (P1 x P2)</td><td>10</td><td>0/30</td><td></td><td></td><td></td><td>0/30</td><td></td><td></td><td></td></tr><tr><td>F<sub>1</sub> (P2 x P3)</td><td>30</td><td>0/30</td><td></td><td></td><td></td><td>0/30</td><td></td><td></td><td></td></tr><tr><td>F<sub>1</sub> (P3 x P2)</td><td>30</td><td>0/30</td><td></td><td></td><td></td><td>0/30</td><td></td><td></td><td></td></tr><tr><td>BC<sub>1</sub> (P2 x P3) x P3</td><td>100</td><td>51/49</td><td>1:1</td><td>0.04</td><td>0.90-0.75</td><td>51/49</td><td>1:1</td><td>0.04</td><td>0.90-0.75</td></tr><tr><td>F<sub>2</sub> (P1 x P2)</td><td>159</td><td>32<sup>a</sup>/127</td><td>1:3</td><td>2.56</td><td>0.25-0.10</td><td>-/127</td><td>1:3</td><td>2.56</td><td>0.25-0.10</td></tr><tr><td>F<sub>2</sub> (P2 x P3)</td><td>149</td><td>33/116</td><td>1:3</td><td>0.65</td><td>0.50-0.25</td><td>33/116</td><td>1:3</td><td>0.65</td><td>0.50-0.25</td></tr></tbody></table>

S/R: no. susceptible plants/no. resistant plants

+/-: no. of plants positive/no. of plants negative

a: dead plants
from the backcross population PI 247087 x (PI 1344117 x PI 247087) which segregated in the ratio 1 resistant to 1 susceptible. This was considered as evidence that the genetic factor in *L. hirsutum* f. *glabratum* PI 134417 is a single dominant gene, to which the symbol *Am* has been tentatively assigned.

*Am* is the first gene identified conferring resistance to AMV in tomato. As the gene is simply inherited, it can be easily introgressed using backcrossing or pedigree breeding. No differences were found in segregating ratios in intra- and interspecific crosses. The resistance of *L. hirsutum* PI 134417 was efficient against several virus isolates from different geographic areas in mechanical inoculation tests (data not shown). Further analysis could give more information about the possibility of using this resistance for breeding purposes by testing advance breeding lines in the field.

Recently AMV has been reported as potentially very dangerous in tomato crops in the south of Italy, mainly due to the appearance of a strain inducing necrosis on leaves and fruits (Ragozzino, 1995; Finetti Sialer *et al*., 1997). The resistance to AMV reported in this study could provide a useful means of reducing such losses.

## ACKNOWLEDGEMENTS

The authors thank Prof. G.P. Martelli and Prof. D. Gallitelli for critical reading of the manuscript.

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